I'm looking for a technical (medical or biological) term for when an animal freezes in response to a perceived danger. This is a pretty well known phenomenon (https://en.wikipedia.org/wiki/Fight-or-flight_response), i.e. a deer freezing in the headlights of a car, but I'm having trouble determining if there's a more precise word/phrase.

1 Answer 1


It is not actually "fight-or-flight" but rather tonic immobility. It is an instinctive reaction in many prey animals which is similar to "playing possum" or feigning death. It increases the chance that an animal's natural camouflage will work to hide it from a predator. It doesn't deter cars, though.

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    The word for an animal feigning death is thanatosis.
    – JLG
    Commented May 14, 2012 at 2:34
  • @spinning_plate Smells like a “bunny in the headlights” paralysis to me, no?
    – tchrist
    Commented May 14, 2012 at 2:50
  • I don't know in what context the O.P. plans to use it, but I suspect most people would be more familiar with the term "playing dead," and perhaps unfamiliar with "tonic immobility."
    – J.R.
    Commented May 15, 2012 at 8:40

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