RUM is pure mind reading. Imagine you can walk up to a total stranger and divine their thought of card in front of them, and it is PROPLESS.
All you need to do is just REALLY READ MINDS.
Spector think of a card and you divine it. Direct and simple.
RUM also allows you to perform ACAAN(Any Card At Any Number) with an Ordinary deck of cards. Spectator just have to think of ANY card and name ANY number they want, and NOTHING is written down.you don't even need to know what card they thought of.
This is not the most easiest things you can do,but it can be your go to effect and it also can be your reputation maker once you get it down.