It's usually easy to tell when something makes me happy. Either I get a contented, sorry-my-insides-just-melted look on my face, or I start bouncing up and down and making a joyful ruckus. Mustelidae, or members of the weasel family, generally illicit the latter response. I love all of these little buggers. They're like liquid encased in fur. Weasels, otters, martens, stoats, mink, badgers, wolverines, ferrets, you name it. Box that up. I'll take it to go! I can't speak for the rest of them, but ferrets have two modes: on or off. You haven't lived until you've seen a ferret do the war dance. The whole family is almost as effective at derailing my train of thought as one of these:
Corvettes get their own special reaction, though. It's something akin to melty insides, but it's more like my brain gets wiped for a few minutes while my head turns owlishly, mouth agape, after those double taillights until they're out of sight.
Listening to: How It Should Have Ended: Lord of the Rings
Reading: Harry Potter and the Deathly Hallows by J. K. Rowling