Pushes the picture around with noise, so it ripples and flows like something seen through moving water.
The idea behind it is worth knowing because it turns up everywhere. Normally a pixel shows whatever is at its own position. Here, before looking, each pixel is nudged somewhere else, and how far it moves comes from a noise pattern. Since nearby pixels get nudged in similar directions, whole regions of the picture stretch and swirl together instead of turning into confetti.
strength sets how far things move and scale sets how large the swirls are. Small scale with high strength shreds the picture; large scale with low strength gives a slow underwater drift.
speed animates it, and it does so by turning the noise in place rather than travelling through it. That means the pattern comes back to exactly where it began, so the motion loops forever without a jump.