Whoopie cushion

A whoopie cushion was a toy that was used as a practical joke. According to Bernice Summerfield, when one sat on a whoopie cushion, it went "phrrrrtttttt".

The High Japester of Beedle placed a whoopie cushion in the Beta Centauran Arbiter's room. When the Arbiter sat on it, he died of heart failure. (PROSE: Beedlemania)

Behind the scenes
A "Slitheen Gas Exchange" whoopie cushion was released as a free gift with the second issue of Doctor Who Adventures.