What caused the hole in Millburn's Helmet?

When the crew returns to the Juggernaut and find Millburn's body, there's a large hole in the faceplate of his helmet. It would appear that something melted the glass and escaped. Yet the Hammerpede was still in his oesophagus, and there is a residue of black goo around the the edges of the hole.

The Hammerpede entered through the arm of his spacesuit, so what caused the hole? If the hammerpede had laid something in his chest then it follows that there would have been a chestburster exit wound. As there was no sign of that, did the hammerpede deposit it's 'present' in his throat and the resulting embryo-burster exited through his mouth, then helmet?