Corny

I filled up the car with petrol yesterday and went to pay. The two girls behind the counter were chatting.
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One said to the other, "Remember when I had a frozen shoulder and you diagnosed it?"
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The other said, "Aye, and I've got no university degrees nor nothin'."
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The middle-aged man who was paying the second girl for his petrol tried to be flirtatious: "I've got a corn. What would you suggest for that?"
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She didn't look at him. She didn't pause for breath. She said, "Cook it."