When the car engine developed a slight knock, the husband asked his wife if she had bought special non-leaded or regular gas, but she couldn't remember.
"You probably got the cheaper gas," he said. "That could account for the roughness of the engine."
"No, the gas wasn't cheaper!" she replied indignantly.
"Well, how much did it cost?" asked the husband probingly.
"It cost the same as always." said the wife.
"I told the man to put in the usual ten dollars worth."