A Fish Called Wanda (1988) Written by John Cleese, story by John Cleese and Charles Crichton.
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Wanda: Ken, somebody just called! They said that the police know that the loot is in a garage in Fulham somewhere. You and I have to go get it right now, Ken. You and I have to go move it before the police find out where it is!
Ken: No, no, no.
Wanda: What?
Ken: It's all right!
Wanda: What?
Ken: Ge-Ge-Ge...
Wanda: George.
Ken: M-m-m...
Wanda: Moved. George moved the loot?!
Ken: Yes.
Wanda: Where'd he move it, Ken?! Where did he move it?!
Ken: K-k-k... I don't know where it is. There's a key. I don't know what it's for. It's in the...
Wanda: Don't tell me. It's better that you don't tell me. Oh, you know, if it wasn't for George...
Ken: Otto... tried to k-k-kiss me.
Wanda: I thought he might.
Ken's stutter could have easily been just a gimmick to get some funny scenes (which we do, in spades), but his speech impediment is cleverly tied to his character development. It shows in this scene as Wanda kisses him and also in the scene where
Ken finally gets his revenge after Otto made fun of his stuttering the whole movie. After Ken steamrolls Otto we get this:
Ken: "K-k-k-k-Ken." You bastard. Hey, I've lost my stutter. It's gone. I can speak. How much wood would a woodchuck chuck if a woodchuck could chuck wood?