flip-turn

A prose poet should meet the margin with same energy as a competitive swimmer’s flip-turn, pushing off the pool wall.

come up for air

In poetry the right margin is not like in a swimming pool, where the swimmer must make a turn against a wall. The line ends where the swimmer in open water comes up for air.

flip turn

Constraint of the verse line: With each flip-turn, a swimmer gains power pushing off from the pool wall.