I grab her tighter and shoot my load in her bum.

He shoots better than he rides.

A perpetual motion may seem easily contrivable.

[T]he fair star / That gems the glittering coronet of morn, / Sheds not a light so mild, so powerful, / As that which, bursting from the Fairy's form, / Spread a purpureal halo round the scene, / Yet with an undulating motion, / Swayed to her outline gracefully.