Mr. Bump is shown to be a large bulky man with brown hair, who wears a blue suit with pants raised up to his stomach, as well as a white undershirt with a black tie and a white hat.
He first appears when he walks to his house, as Duncan mistakenly beileves him to be an assassin due to him looking so suspicious, almost exactly like a guy from the movie, Nosy Neighbors, which he was watching to pass the time while he recovers from a cold that prevented him from going to school. He appears again when he hears that Elmyra's Grandmother had reportedly passed on over the phone, a rumor started by Elmyra telling Nurse Klienerman that Grandma passed away, when it was really her pet hamster, Jan Brady. For the rest of the episode, Duncan had also beileved that Mr. Bump killed his Grandmother. As Elmyra goes into Mr. Bump's house to invite him to the funeral for her pet hamster, Duncan worries that Mr. Bump might kill Elmyra next. As Elmyra encounters Mr. Bump, Duncan swings from his room to his kitchen, only to have Elmyra scold him for not being in bed to recover. Before they leave, Elmyra tells Mr. Bump he is invited to the funeral. He later appears towards the end of the episode when he returns the box Grandma Duff left on his yard, which has a nightshirt inside. When Grandma makes it sound like she tried to seduce him, Mr. Bump then runs off in fear.
- Mr. Bump is the second character to be voiced by Frank Welker but be uncredited for it, the first being Count Blood Count.