Cat question

What do cats sense when they crouch down and scurry around for no apparent reason? Are they sensitive to tectonic movement that we are not tuned into to? Thanks

I think cats often hear or see what they think is a small rodent eagerly waiting to become their next meal. Sounds which trigger it tend to be sudden rustling, often the kind of rustling which starts and stops without warning. Jerky movements from unknown sources will also make a cat perk up; the cat is usually less interested if a human is known to be doing the moving. So, perhaps a dust bunny has blown across the floor in a mousy sort of way, that makes the cat go into stalking mode. Or perhaps a cellophane bag has been moved by accident, which is a sound sort of remiscent of a small critter running across floor boards. In any case, a lot of things that humans barely notice stand out like neon signs to cats (and vice versa).