A certain species of desert lizard digs tunnels in which to lay its eggs  The eggs must incubate inside the tunnel for several weeks before hatching, and they fail to hatch if they are disturbed at any time during this incubation period
Yet these lizards guard their tunnels for only a few days after laying their eggs
The only way to disturb the eggs of this lizard species is by opening up one of the tunnels in which they are laid.