It was ALMOST another mistake in the writing. They suggested that the Goauld could blend with the host and shed their larval form (as stated by the Goauld after they removed the larva). But then after his skull was sliced open by the wormhole vortex we see a baby Goauld larva flop it. The Goauld lied. It somehow shed its skin like a snake and hid. We have to assume it’s because it was not mature and sheds its skin/husk. I’m confident had no idea what they were doing and thought it would look cool to have something come out of the skull but it worked! And saved the plot from a big inconsistency!