Not to be confused with https://tvtropes.org/pmwiki/pmwiki.php/JustForFun/ChekovsGun

Linking to 5 tvtropes pages —5 possibly-very-deep rabbit holes— on a generally nonworking day? Truly diabolic :D

The image in the first link points out that there is a literal rifle on the wall in Shaun of the Dead. That's a pretty cool reference to the origin of Chekhov's gun.