How do we react in traumatic situations? Most of us are familiar with the age-old formulation of "fight or flight." Under stress, or confronted by an imminent threat to our survival, traditional psychological theory says that most of us react in one of two ways. We either fight or flee, depending on the relative size and advantage of our assailant. In these life-or-death moments, our hormones kick in, spurring us on to battle or inspiring us to run away.

Sexual assault survivors often face doubts when they step forward. "Why didn't you fight back, or scream for help?" "Did you struggle?" Many survivors also ask themselves these painful questions. Some even come to believe that they are at fault for what happened to them, wondering how, in a life-or-death situation, they were unable to struggle or free themselves from the grip of their assailant.

Across the country, resistance is still considered the "normal" reaction to sexual assault. In some jurisdictions, this understanding is even baked into the law. A few states continue to define rape in relation to active resistance, believing, mistakenly, that any reasonable rape victim would fight back against their aggressors.

These erroneous, and damaging beliefs, have been with us for decades, if not centuries. But a growing body of new research suggests that most, if not all, sexual assault victims do not fight back. Many do not yell out for help. In these perfectly-normal cases, victims do not resort to their fight or flight responses. Instead, they freeze, experiencing what experts call "tonic immobility," a very real, and very terrifying, physical and mental reaction to extreme trauma.

In recent years, trauma researchers, including those schooled in our natural reactions to sexual assault and childhood sexual abuse, have identified a third form of response that sits in between fight and flight. The traditional view of "fight or flight" is outdated. Instead of clenching our fists and preparing for combat, or attempting to run from the scene, many of us undergo a third "freeze" response in the face of trauma or imminent harm.

We feel stuck to the spot. Our bodies grow rigid, as our breathing slows. In some cases, we even become physically cold or numb. A sense of dread or inevitably takes hold. And mentally, we leave, dissociating from the present moment.

This "freeze" reaction is particularly common in cases of sexual assault, when victims have been physically overpowered by their abusers. It can also happens, sometimes in a temporary form, when an abuse victim first realizes that an attack is imminent. The brain is "shocked," like being thrown into a bucket of cold water, by the understanding that harm is on the way. It's not uncommon to hear sexual assault survivors say, "I froze for a moment," when their assailant forcefully grabbed their arm, ripped open their shirt or flashed them a menacing look.

After an attack has started, the freeze response can ramp up, taking utter control of a victim's mind and body. The brain, in these crucial moments, actively "resets" itself, according to Jim Hopper, Ph.D., a clinical psychologist who specializes in victims' rights work. And this is all utterly out of our control. No one chooses to enter a state of tonic immobility. It happens to them. There is no shame in having frozen, because there is no responsibility. It's just the way that, in many cases, our bodies respond extreme fear and stress.

In an article for Psychology Today, Dr. Hopper explains how the freeze response becomes clearer through reference to evolutionary theory. Many animals, including rabbits and deer, freeze after encountering a threat. The body seizes up. So, it turns out, does the brain.

In the context of non-human animals, freezing serves two purposes. On the one hand, a non-moving animal is harder for a predator to spot. Frozen in the woodlands, a deer or rabbit draws less attention. At the same time, freezing, both mentally and physically, puts a stop to whatever behaviors and thought processes were going on before the threat was recognized.

That opens up physical and mental space to contemplate and decide on new behaviors, ones that could neutralize or evade the threat to one's survival. This mental and physical "reset," Hopper writes, "prepares the brain to receive new and potentially life-saving information - and generate options for responding it." Most survivors seem to remember this stage of the freeze response, Hopper says. They may remember being in shock, or their minds going blank. However it's experienced, this phase of freezing is "a helpless and horrifying state of being."

As the attack continues, our body continues its unconscious work, but, in many cases, it's not geared toward fight or flight. In many cases, sexual assault victims are entirely overpowered by their assailants. For all intents and purposes, the possibility of escape, or resistance, has been removed. There is no reasonable way to fight back. The assailant has overwhelmed your defenses, leaving you helpless. And "fight or flight," which would normally kick in at this moment, are both impossible.

At this point, our brains fall back on reflexes and habits. During a sexual assault, there's little time for rational thought. The brain has frozen in place; faced by a larger and stronger assailant, it skips, like a record. If we had time, the brain could latch onto our memories and rational capabilities to develop a plan of escape, or a response that could lessen the assailant's aggression. Our brains, however, don't work like that.

Overpowered by an imminent threat, terrorized by fear and anxiety, the brain shifts away from rational thought toward reflex. Even the slightest error or misstep could mean the difference between life and death, so our body needs to rely on split-second decisions. That's the realm of habit, behaviors and reactions that have been drilled into us over the course of years.

But apart from some highly-trained members of the military, most of us haven't been trained to deal with life-or-death situations. So we stay frozen. There's no time to think of rational responses to the trauma, because our brains have shut down rational thought for the time being. But there are no pre-loaded emergency responses for our bodies to switch to. In the end, we're stuck in limbo.

When thought does return, it can be just like that warped record we mentioned before, skipping over and over the same simple thought. "Why is this happening?" "God, help me." "He'll finish soon." Thoughts such as these repeating again and again through an otherwise-blank mind.

Under these circumstances, freezing is a perfectly normal reaction. It is not a sign of weakness, or evidence that you "wanted" to be sexually assaulted. Far from it. In fact, freezing in the grips of an assailant may be the "best" option, according to authors in Psychology Today.

Fight and flight are no longer options. With an assailant controlling your body, there is little hope of escape and, for most women, who comprise the majority of sexual assault victims, no hope of fighting back. And, during a sexual assault, there is no reasonable way to process, or resolve, the immense terror and fear that have paralyzed you.

Freezing, and mentally dissociating from the event, becomes the only avenue for escape. Even though we cannot escape physically, the hope is that we escape, in some sense, mentally. This is the effect of the freeze response, numbing us, both physically and mentally, to the assault.

In fact, some of our hormones may come to our aid in this situation. Endorphins, a class of hormones closely linked to morphine and other opioids, act as an analgesic, numbing us to our surroundings. Our brains kick in, whether or not we want them to, "by blocking out what's much too scary to take in."

Understanding the freeze response helps to explain why sexual assault survivors often struggle to remember key details from the assault. It's because they left, metaphorically, for the duration of the attack, numbed by their body's natural response to severe terror, panic and anxiety. But as we've seen, the "freeze" response, tonic immobility isn't just a mental response to trauma. It's a real, physical reaction, one in which our bodies literally lose the ability to move or speak.

Nor is tonic immobility rare. A number of recent studies have found that feelings of paralysis, numbness or being mute may in fact be the norm. A 2005 study published in Behavior Research and Therapy, for example, found that an estimated 52% of undergraduates who reported childhood sexual abuse experienced some level of paralysis during the attack.

Even newer research out of Sweden lends credence to earlier results. In a paper for Acta Obstetrecia et Gynecologica Scandanavica, researchers at the Karolinska Institute found that, among 300 women who visited a rape clinic, almost 70% reported "significant tonic immobility." Nearly half of the women were diagnosed with having experienced "extreme" tonic immobility. While this area of research is still new, it appears from these preliminary reports that "freeze," the state of tonic immobility, is not at all rare.