It seems that if they're high a lot - eg., 400s and up - even mid-200s "feels" low to their liver (using the simple description). That can trigger a bounce. Not only that: a more rapid than usual drop even if it's from, say, 500 to 300 can trigger a bounce. So it's not just going lower than they're accustomed but how quickly they drop that can be the culprit. Teasel reacts this way.
I've also noticed what I call Teasel's "feel good" numbers. He seems happiest, perkiest, etc. when he's 8 - 10 (approximately 150 - 180) and quieter when he's too high or too low. It's not easy to get a tricky cat to the level that seems good and have him surf there. If it was, I'd try to have Teasel sitting between about 6 and 10 every day. Wishful thinking ...