Gaspode

Gaspode is a small terrier-like dog featured in seven of Terry Pratchett's Discworld novels. He possesses human-level intelligence and the ability to speak, as well as an extensive collection of diseases (including 'Licky end' which is only found in pregnant sheep); he claims that the only reason the diseases haven't killed him is that they're too busy fighting amongst themselves to focus on him. However, since everyone knows that dogs can't speak, people tend to interpret his speech as their own personal thoughts, a tendency which Gaspode regularly uses to wrangle food from passers by. (In fact it has been mentioned in the books that a passerby kicked Gaspode into the gutter, and had gone no more than five steps before he thought "I'm a bastard, what am I"). The exceptions to this are Carrot Ironfoundersson (who eventually figures out the truth himself), Angua (who he tries to court because she's a werewolf), the staff of the Times (who he needs to pass some information to), and the... full article at wikipedia