An African horsefly called Tabanus lays eggs in pools of water in which the larvae live and feed. Each larva buries itself in the mud and pupates. As mud dries out, it cracks, and there is a risk that a crack will tear right across the grub's refuge. Before burying itself in its own pupation chamber, it first corkscrews its way down into the mud in a spiral. It then corkscrews its way back to the surface in an opposite spiral. Finally, it dives into the mud straight down the centre between the two spirals, and that is its resting place through the bad times until water returns. Therefore the larva is encased in a cylinder of mud whose circular boundary has been weakened in advance by the preliminary spiral burrowing. When a crack snakes across the drying mud, if it hits the edge of the cylindrical column, instead of cutting straight across the middle it goes instead in a curved bypass around the edge of the cylinder, and the larva is spared. (I told you you should read Dawkins, LH. It's not boring.)