The other volunteer has the helmet for the Psych-O-Matic placed upon them. Volunteer number 2 places foam earplugs into their ears. A sound-effect cue is played to indicate that the machine is working. The volunteer is announced to now have psychic powers. After receiving a test psychic message from the performer, the volunteer is able to correctly determine the chosen celebrity.
The helmet is removed from the first volunteer and smoke billows up from their hair.
A variety of methods and presentations allow you to tailor this hilarious impossibility to suit your own act.