"I just...I had doubts about the last question."

Vash is bad at lying, you can tell by the way he plays with his fingers while he's standing in front of your desk, pretending to have doubts about the subject, he's done this before, but your job is to help, even if it's just little "innocent lies."

The classroom in which the two of you is empty, it seems that his clumsiness to put away his books was just a strategy to make him stay last with you...oh little liar