A mouse feels panicky. It freezes; its little nose twitches. Something is in the air, and it doesn’t like the smell of it. Not one… little… bit.
In mice, the scent of predators causes a surge of stress hormones to course through the blood and induces behavioral changes. Quite a lot is known about olfaction in mice—Richard Axel and Linda Buck split the Nobel Prize in 2004 for elucidating the organization of the thousand or so unique odorant receptors expressed by the sensory neurons in those little noses.
But the neural circuits that transmit a threatening scent from the nose to the hypothalamus, where the stress hormones are released, were not known. Until now.
The majority of predators a mouse is worried about are sight based predators, and they are (almost) hard-wired to follow motion (think your cat with a laser pointer red dot). Freezing until you know where the predator is is almost certainly a survival trait. Hard-wired to follow motion, and much more capable of seeing motion. A mouse could be practically invisible against the background — until it moves and then it’s camouflage could be rendered useless.
Works in humans much the same way. At least, I know there have been many, many times where a bird was right in front of me and I didn’t know it, until it moved. This is part of why blinking lights for cycling came about – solid, always on, lights don’t attract attention if they don’t move fast. The blink/strobe makes the movement pattern more erratic, in hopes of making cyclists at night or low light situations more obvious.