Dogs. They're the one animal I can actively get close to daily which depending on upbringing can either be very loving and sweet, or absolutely territorial monsters.

When I was in high school there was one of those dogs, he'd bark lightly, or his front paws on the picket fence and wag his tail extra hard, which are normally signs of wanting to be pet, except if you got within petting range he'd go for a bite.

Cat's at least get away from you if they don't want attention. I've learned more about dog body laungauge since high school, but I've also been bitten since then on just a random walk by (not going for a pet) just as the owner was saying it didn't bite. It did.

Though I suppose terrified it's a bit much. Wary is more like it.