When Charlie first explains his job, he says that he tells customers that "Fire, theft and casualty are NOT things that only happen to other people." Yeah, that's because he inflicts those things on the people that he's talking to
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When Charlie explains why he doesn't go to a doctor for his ear infection, he says "What's he gonna do? Can't trade my head in for a new one."
When Charlie is talking about the awful day that he just had, he says that he decided to "knock off early" and see a doctor about his ear. Maybe I'm reading too much into it, but that sure sounds like it might be a decapitation pun
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Shortly after, he says, "you've got a head on your shoulders, and what do they say... where there's a head, there's hope."
When he's carrying the lady's body, he bumps her head into the dresser.
Charlie tells an in-shock Barton in the bathroom to "get it out of your head" and, later, reassures him that everything will be all right by saying, "We just gotta keep our heads."
Finally, at the end of the film, he repeatedly yells "I'll show you the life of the mind," which doesn't seem to be a pun or a joke, but further suggests that Charlie is obsessed with heads and minds and that the other references are not coincidences.