Bog monster was a term used by Mickey Smith in March 2006 to refer to Sip Fel-Fotch Passameer-Day Slitheen, who he saved Jackie Tyler from after the Slitheen revealed himself having used the skin suit of Strickland as a disguise. Shortly following the incident, Mickey paranoidly suggested that anyone they could tell of their ordeal had "bog monsters" inside them as well. (TV: World War Three)
On Christmas Eve that year, Mickey alluded to the Slitheen incident when he beseeched Rose Tyler to "just let it be Christmas". (TV: The Christmas Invasion)