I've seen them walking backwards, too. Also they sometimes go through the motions of putting logs or food into the relevant bin while facing away from the bin.

I like their expressions, as well. There's one guy who, when I pick him up, has an expression of complete and utter amazement on his face. He must have a short memory as I tend to use him for special tasks just to see his expression. You'd have thought he'd have got used to it by now. He's also often loafing about "bored" so maybe he's a little simple.