Clary: It's Simon. He's missing.
Magnus: Ah. Missing what, exactly?
Jace: Missing, as in gone, absent, notable for his lack of presence, disappeared.
Magnus: Maybe he's gone and hidden under something. It can't be easy getting used to being a rat, especially for someone so dim witted in the first place.
Clary: Simon's not dim witted.
Jace: It's true. He just looks dim witted. Really his intelligence is quite average.