Various sexual references throughout. In general though, it doesn't rely as much on sex jokes as other shows on [adult swim].

With the first two seasons, there really isn't that much to complain about aside from some slapstick and mild blood. There is a scene in Season 1 that is particularly violent, although it looks pretty fake. Season 3 is where it starts having a little bit more blood, though still comical. Any episode from Season 4 or 5 can feature extremely graphic depictions of gore, such as getting eyes pecked out by crows or pulling intestines out of an open chest. All of it is intended to be funny.

While there's certainly not as much as other shows, that doesn't mean there isn't any. Profanity is used all throughout the series, although anything worse than ass gets censored.

(Note: I don't own the DVDs, so I'm not sure whether it's uncensored on them.)

There isn't any drug use in the show, but there are some references. In one episode, one of the characters is wearing a marijuana symbol shirt, in another, they go shopping at a bong shop, and in another, they participate in a fake interview about the show in which they state that drugs are used in the production of it. (It should be noted that in real life, no drugs are involved and this scene is just a joke.)

Any of the violent scenes might be considered scary to some people.