born bad

i came across this movie in tv today and by the beginning they use a song a character sings in the movie natural born killers and is listed as born bad in the soundtrack.

was i the only one noticing this? they actually took what the character was singing in the scene (that ended up appearing in the soundtrack album) and inserted into this movie...

i was like "whaaa??"
have you ever noticed something similar in, perhaps, another movie? taking audio samples from other movies and using as soundtrack? (not counting roars and stock noises of course)

one may argue that "if it is in the soundtrack album, it is considered a song and, therefore, they can use it if they pay for the rights" but it is so weird...