It is the one where Daffy Duck is trying to impress a girl. (I turned it on halfway, so I didn't see the title). Well, he blows up two balloons that say 5,000 pounds. When he lifts it up someone says something about how he lifted up 5,000 pounds. But he didn't. Both of the balloons said 5,000, so technically he lifted up 10,000.
I am surprised I never picked that up. I mean this is one of my favorite Daffy cartoons and I hadn't realized that he was actually lifting 10,000 pounds. By the way, the name of the cartoon was "Muscle Tussle."