My patronus is a jarvey. It very strongly resembles a ferret, except for one defining trait-- the jarvey talks. Mostly they just a curse, but I would say they are quite different from a normal muggle ferret.
When I feel the chill of what could be a dementor, I fire my jarvey at them and he gives them a ear full.
The trait that the jarvey and I share is bad language and craftiness. I am sneaky when I comes to searching for items that are being concealed from me. Bad language is pretty self explanatory, although I try very hard to keep it to a minimum. Like today, I was chopping up burning roots (pepper jack cheese) for a potion (salad) when a fleck of the root popped into my eye. Needless to say, I did not control my language.
Jarvey are pretty handy to have in a garden to control the gnome population, also!