In Bolognius Maximus when dib and zim are trying to find a cure together about thier bologna problem, dib attacks zim for getting him more bologna-like and falls down a tube. BEFORE they fall down it Zim HAS his lifepack (backpack)

on, but then in the tube it dissapers! Its also not there when they fall out and beat each other up. But when they run away from the dogs, its back on again!!