The doorknob is a recurring joke found in Mother 3. It makes its first appearance in Chapter 1; when Thomas is trying to get Flint to help him, he accidentally rips off the doorknob. It is then tossed and ends up lost. The doorknob then travels around the game's world as the story progresses, usually in some funny way. The player will have to do a lot of exploring to find it in every chapter, however. It can also be found at the "End" screen as an item.
While Thomas is trying to open Flint's locked door, he pulls the doorknob, and it ends up getting loose. Thomas gazes at the broken item as Flint opens the door to see what's happened. Scared of his appearance, Thomas throws the doorknob and hilariously calls Flint "Doorknob", before correcting himself. The flung doorknob knocks on the top of Boney's doghouse, startling him. It then ends up behind a wall, not being seen again until the next chapter.
While heading to Osohe Castle, Salsa finds the doorknob in Nippolyte's "Potatoto" patch. Fassad immediately takes it from him and throws it, telling him "not to pick up strange, doorknob-ish things".
An NPC in the jail in Tazmily Village tells the party that he was arrested for stealing a doorknob, while proclaiming all he did was pick it up.
At the beginning of the chapter, an NPC tells the party that he found a doorknob the other day, but he was frustrated at the time, so he threw it far to the east, dislocating his shoulder.
Near the end of the game, the party can find the doorknob, but they accidentally drop it, and it won't be seen or found until the "End?" screen.