The scene I remember most vividly is one where Butch and Sundance are perched on a ledge atop a cliff. They're being pursued, and the only way ahead is to jump into the churning and angry waters below. The exchange at that point is as follows:
Butch Cassidy: Then you jump first.And they jump.
Sundance Kid: No, I said.
Butch Cassidy: What's the matter with you?
Sundance Kid: I can't swim.
Butch Cassidy: Are you crazy? The fall will probably kill you.