This morning, I want to tell you about a story that’s difficult to read but also eye-opening. Jen Percy, a contributing writer for The Times Magazine, has spent months reporting on a frequently misunderstood aspect of rape — why victims often freeze rather than scream or fight back.

Jen’s story opens with a list of examples, some well-known and some from her reporting. “I froze,” said a woman who was assaulted during a military training exercise. “I just absolutely froze,” the actor Brooke Shields said, describing how she felt while being raped. “I just froze,” Lady Gaga said, about being assaulted when she was 19. “I was like a dead person,” Natassia Malthe, a Norwegian actor, said. One study of rape victims at a Boston hospital found that more than one-third of them reported experiencing a version of this freezing, which in its extreme form is known as “tonic immobility.”

Researchers say that it is an automatic defensive response with roots in evolutionary behavior. There is a cliché, dealing with a different kind of threat, that captures the same idea: a deer in the headlights. Jen writes:

For more than a century, scientists have studied similar phenomena in animals, and over the years they have been named and renamed — animal hypnosis, death feigning, playing dead, apparent death and thanatosis, an ancient Greek word for “putting to death.” Tonic immobility is a survival strategy that has been identified across many classes of animals — insects, fish, reptiles, birds, mammals — and draws its evolutionary power from the fact that many predators seem hard-wired to lose interest in dead prey. It is usually triggered by the perception of inescapability or restraint, like the moment a prey finds itself in a predator’s jaws.

As Amy Arnsten, a neuroscientist at Yale, says, “Under stress, your brain disconnects from its more recently evolved circuits and strengthens many of the primitive circuits, and then these unconscious reflexes that are very ancient kick in.”

Yet many people remain ignorant of the frequency of freezing during sexual assaults. Instead, friends ask victims why they didn’t fight back or yell for help. Doctors and nurses are sometimes confused, too. Most significantly, police officers have long treated reports of freezing as a basis to doubt an assault allegation. That attitude is one reason that such a small portion of reported rapes lead to criminal charges.