Both my cats, and every other cat I’ve observed, when hunting, will crouch down, then wiggle their butts in a distinctive way just before the pounce. It seems to be an instinctive behavior, like shaking their heads to break the prey’s neck as soon as they grab it. What is this for? My husband theorized that maybe they’re “digging in” their back paws to be sure they’ll have traction for a leap.
It seems like smart prey might learn to react to this. I certainly have learned that it’s time to jerk the mouse-on-a-string across the floor when I see the Butt Wiggle commence (unless I’m letting them get an easy catch for some reason).
Any ideas?
I don’t know, but I knew exactly what the thread was going to be about before I opened it, having observed the feline butt wiggle many times. 
Your husbands idea sounds right to me.
This was answeed in a previous thread.
I believe it is something to do with ‘warming up’ their muscles before the punce, in the same way we’d warm up before exercising.
That’s what I was told, once, long ago, anyway.
Dogs wiggle their butts sometimes, too, but for vastly different reasons.
As part of their greeting ritual, both of my friend’s Pembroke Welsh Corgis (small, long dogs with no tails) bow down to the person and wiggle their butts while holding them in the air. This wiggling can get to be quite intense, to the point where they are almost approaching the newcomer sideways.
I’ve never seen any other dog do this, come to think of it. Maybe it’s just a quirk of those bizarre little dogs.