First pip.

This photo shows one of the eggs in the incubator which has just started the hatching process.

The build up of CO² in the egg has caused the chick inside to jerk its head involuntarily.

At this stage, the beak has a small hard protuberance, known as an egg tooth, on the tip, which initially breaks into the air sac in the round end of the egg, and later to start breaking the shell. This is known as "pipping".

The chick develops in the egg curled up, and as the hatching process develops, it slowly unwinds, and makes a series of "pips", eventually breaking away the blunt end completely (a bit like a soft boiled egg!), enabling the chick to hatch.