In the episode "Wallaby on Wheels", Rocko tries to impress Sheila by completing the obstacle course at the skating rink. As he completes it, a crowd forms at the bottom. The shot goes to something else for a second. When it comes back to the crowd, Sheila's tail is missing. This is probably only visible for a split second, but since I haven't seen this episode in about a year, I don't know how long it lasts