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so your last comic made me really think....have the egg-eaters ever gotten an egg that maybe was a little too incubated? Like, what's the rate of growth in those things? Do they eat them while they are still new? Does Matthias have a system to ensure they DON'T become incubated? Has a half-formed hatchling ever popped out after the first bite? Would they even care? (looking at Rannoch...)
To answer your question: It happens VERY, VERY, rarely. For example, the incident with Via.
Y'know, I've always imagined the eggs being mostly goop until the last few hours of formation. On one hand, having a full incubation cycle where the hatchling grows steadily is more, uh..."scientifically faithful" to how eggs work.
On the other hand, goop magically evolving into a dragon within the egg shell at the last second sounds like a cool process. It could be observed as a little flash of light from within the shell a few days before hatching. I'd say, 90% of the time the insides are magic goop, and the last 10% is the flesh and blood stage.

The Gang keep their eggs fresh by simply 'not incubating' them, and it hasn't been a problem yet.