Crazy mixup

I admitted a guy to hospital a little while back.  He had liver failure and severe abdominal distension, probably due to his alcoholism but possibility of an intrabdominal malignancy couldn't yet be excluded.  A little while later my registrar walked into the cubicle to find me whipping the patient's stomach with a leather thong and making him wear a hair shirt.

"What are you doing?" shrieked my registrar, "I asked you do do an ascitic tap!"

"Oh!" said I, "I thought you said an ascetic tap."