A colon check uses a long, bendy tube with a camera. The colon is not a straight pipe — it curves, folds, and can stretch.

When a doctor pushes from outside, the middle of the tube can loop (form a curve that eats the push) instead of moving the tip forward. The tip can also drift. Then folds of the lining hide spots that should have been seen.

Incomplete looking is one reason early growths get missed. Prep quality and careful withdrawal time matter too — but instability is a real mechanical thief, not a “lazy doctor” story.

The tube is useful because it bends. That same bendiness is why thoroughness is hard.