Over a steep drop, and then thunk, your bow strikes rocks lurking in the froth below.
All forward movement stops.
Pain radiates through your feet, ankles, and knees. It's hard to breath. You let go of your paddle. The dynamics of the vertical pin with entrapment can be easily simulated by leaning a kayak against a grassy vertical slope of 45 degrees or steeper. When we first tried this exercise as part of a river rescue clinic, we were astonished by this discovery.