Since Charms was one of his favourite classes, Drew made sure that he was sitting upright and paying attention, he even had some parchment and a quill in front of him. The Professor's question had him thinking for a bit, it wasn't an easy question because he was an open person and didn't know how to be sneaky.

"There's invisible ink." he said with his hand raised. "You can hide messages so that only the intended person could read them."