Linus's blanket apparently stayed shredded after Snoopy tried the trick where it would be put back together again, yet in the next shot, his blanket is perfectly fine.
When Charlie turns invisible, the Great Houndini pokes the spot where he was standing with his wand, and it goes through thin air. But Charlie is invisible, not intangible, so the wand would have bumped into him and given the game away.