Nice
I was thinking the same thing while watching that movie.
Some friends tried this on me once at a sleepover when I was younger. They woke me up while doing it, so I pretended to keep sleeping and let them do their thing. They kept dipping my hand in and out of the bowl of water...so I shot up real fast and yelled "blah!", which scared the crap out of them and the guy with the water dumped it down the front of his pants. Back fire.