Sonny's friend, Mr. Herlihy (the role listed as Old Man in the ending credits), is named after the film's co-writer Tim Herlihy who coincidentally plays the singing kangaroo.
In the scene where Sonny and Julian are warning roller-bladers to "slow-down", they are standing about a few feet away from each other. When the homeless man comes by in a shopping cart, they appear to be standing further apart. When it cuts to them again (after the homeless man has passed them), they are standing close to each other again.
When Julian spills the milk on the floor the milk is spreading towards the back of the room. Then when the camera switches back to Sonny the milk is a circular pool before Sunny put the newspaper on it. The newspaper never gets wet.
When "Frankenstein" vomits on the floor, it is partially on the floor and partially on the carpet. Later, it is totally on the floor with none on the carpet