What exactly is a 'flinch' anyway?

So several nociceptive assays, such as the formalin test or capsaicin test, score the behavioral responses to injection of an algogen. Typically, the behavioral measures scored are biting, licking, or lifting. These are fairly straightforward to define. It’s clear when a mouse puts its paw in/near it mouth, or is holding it up from the floor surface. But I also see flinching used as a measure.

Flinching is defined as:

make a quick, nervous movement of the face or body as an instinctive reaction to surprise, fear or pain.

OK. So what is that in a mouse? Is that a rapid withdrawal of the paw? Does speed of movement define this behavior?

If anyone has a video or good description of what they qualify as flinching, it’d be great to see and share.

Mice flinch way less than rats. Check out this very old paper: Sufka et al., Eur. J. Pain 2:351-358, 1998.