hmmm, just wanted to make sure since the OP said only one post...but i'm sure i can come up with more wacky ideas ...like a large immoooovable cow (lol)
I enjoy hearing these guesses so how about this: you can guess once per day until the contest is over.
How many winners will there be if nobody guessed it right? My guess: A hangnail that you can only pass through by biting it off.
i've got more: a car tyres a fire that you need to jump over a flying bird that you need to kick down or else it poops on ya