I have noticed this as well. A group behaves very differently from a pair. And a single shrimp acts like a very lonely shrimp. I think I've said it before, but basically I'm amazed at how dynamic the social structure is for them, being that they're basically "bugs" I think we tend to give them less credit than they deserve.

Having now seen the dynamics of group behaviours of them, I'd never again try shrimp unless I got *at least* 4 of them. It's really neat stuff.