Whoopee cushion
From Academic Kids
Whoopee-cushion.jpg
Whoopee Cushion
It is used by inflating it and placing it on an unexpecting victim's chair. When the victim sits down, his weight squeezes the cushion, causing it to sound. It is unlikely that observers would mistake the sound of a whoopee cushion for the victim actually flatulating; much of the humor is in simply taking the victim unawares.
A recent twist is the self inflating whoopee cushion, these contain a foam sponge so that after use they reinflate.
More recently, electronic devices that produce pre-recorded farting noises have been sold; these are usually timed or remote controlled. This means that they can be activated well after the victim has sat down, and thus have more likelihood of being mistaken for an actual fart.
