And as an fyi for anyone that may be confused: They mean the patient squeezing a rubber ball while their arm is in a tourniquet (the band that goes around the upper arm while blood is drawn).
(But yes, either type of ball is completely different than squeezing a penis. Just goes to show how screwy perception can get while under anesthesia.)
One of the requirements for Brannigan’s law is that you can’t make it obvious that you’re invoking it.