A Concussion.
A: Without him the fiddle would be the most hated instrument on earth.
Because no one on earth wants to buy it.
Lady: I forgot the name, but is starts with 'T'. Sardar: Oh, what a strange car, starts with Tea. All cars that I know start with petrol.
Because they make up an awful lot of stuff. EDIT: Because I forgot about neutrinos.
He looks for fresh prints.
Look for fresh prints.
A: So they don't get a concussion while bobbing their from head side to side as they are saying "I don't know " whenever you ask them a question.