I have grown tired of coming up with clues so here is the answer to the riddle. It was rainy and the leaves were falling the day that we were in the van and I came up with the riddle. Some leaves had fallen on the wet van and stuck fast. The leaves only came off (reluctantly) when I used the windshield wipers. None of the leaves blew off on their own. The wind wouldn't even blow them off. The leaves that were left on only came off after they had dried completely.