Black Magic is also a party trick that needs two (or more) people in on it to accomplish.

In a nutshell, Person A (who knows the trick) leaves the room, while someone/everyone else in the room picks a secret object. When all the picking and choosing is done, Person A gets called back in. Person B (who also knows the trick) then proceeds to name off various objects in the room, eventually picking the secret object. Person A, if ey has been paying attention, sucessfully picks out the item

You see, the trick is to have Person B say the name of something that is black before the secret object.

Example:
Person A leaves the room.
Random People: Ah-ha, let's pick this cup!
Person B: Person A, come back in!
Per. A enters the room, stage left.
Per. B: Is it...this microwave?
Per. A: No.
Per. B: Is it...this monkey?
Per. A: No.
Per. B: Is it...this pot(this pot is black)?
Per. A: No.
Per. B: Is it...this cup?
Per. A: Yes!

Hopefully, this will make people irritated and confused.

Note: you should not tell people how to do this trick. They should figure it out themselves.