Domesticated animals' personality traits seem to correlate with physical characteristics.

Dogs are more attuned to cues from humans, if they happen to live with humans. Boy, that's such a shock I'll have to add an item to my to-do list.

Fall ... off ... chair.

The interesting thing is that it's genetic rather than "socially" acquired.

A friend who raises rats says the same is true of them; "hooded" rats (with what amounts to a large spot on the head) are the best ones when it comes to human companionship (she wrote this while a rat was asleep on her shoulder).

There was a paper in Science a few years ago about a Russian study where they tried to domesticate foxes. As they selected for friendlieness towards humans one of the side-effects was that the foxes's ears got floppy.