Figure 1. A 42-year-old man with a history of mild, intermittent pain on the lower left side of the abdomen presented with an episode of painless hematochezia. The physical examination was normal, and his hematocrit was 44 percent. Diverticulosis of the sigmoid colon (Panel A) was revealed during flexible sigmoidoscopy for evaluation of the bleeding. There were multiple diverticula and a 1-cm sessile polypoid lesion (Panel B) that was the same color as the surrounding mucosa. The polyp vanished with the application of gentle pressure from the tip of a closed pair of biopsy forceps, confirming that the lesion was . . .