A long time ago I worked with a local concreter and we were doing new concrete tennis courts in Toowoomba and a bloke with us tried to take his jumper off while holding the handles of the whirlybird between his knees. Well it go away on him and as the handles spun around the machine started to rock from side to side and dug a hole through four inches of concrete. He wasn't very popular and no it wasn't me.