when a doctor (or anyone) examines your rectum by sticking a (hopefully) gloved finger or two up your ass.
Joe went to his yearly check-up with no clue that he was mere minutes away from losing his anal virginity.
Rectum? It damn near killed him!!!
An exploration of the anus, colon and large intestines either digitally(a "finger wave") or by a Sigmoidoscope (the "Silver Stallion") to detect polyps, pre-cancerous lesions or early cancer.
Don't believe the proctologist when he tells you that you'll only experience mild discomfort when they video your colon...it feels like they sent an angry dwarf up your ass with a camcorder strapped to his spiked helmet.