no humor
3 riddles
the first two are old
the third one i made up
i cant vouch for the Halachic veracity of the answers
1. two actions are assur, done together they are both mutar
2. two objects, one is mutar, one is assur. when brought together the mutar item becomes assur. the assur item becomes mutar (nothing to do with the parah aduma)
3. two “items” are brought together, one is kosher one is assur. the kosher item becomes pasul. the asur item becomes mutar (nothing to do with the Parah Adumah)