When Bobby kicks the young john out of the hotel after robbing him Helen is loosely using the towel to cover her breasts. In the next shot the towel is wrapped neatly around her.
(at around 15 mins) When Bobby asks Helen to do him a favor, his hand changes position between being under his hair on his forehead and being on top of his hair.
The opening text of the movie that sets the location of Needle park at Sherman Square says that it is at the intersection of Broadway and West 72nd Street. In actuality, Sherman Square and the exact location where the addicts hang out is at the intersection of West 71st street and Broadway.
[45:50] Boom microphone (and camera) visible in the upper right hand corner near the end of the stick ball game.