Appearances can be deceiving

The student sat in the back row. He didn't seem to be paying much attention to the lecture. His arms were folded, his legs splayed out, and he looked like he was catching up with some sleep.

The lecturer posed a problem involving some tricky mental arithmetic. The student didn't stir.

The lecturer asked the students for their attempts at solving the problem. Some of them had got part of the way there, but they hadn't managed it fully. A hand gradually raised in the back row.

"Yes?" The student in the back row gave the correct answer, still slumped in his chair.

Moral of the story: just because they look like they are asleep doesn't mean they aren't paying attention!