((there was some confusion over what’s going on in this response, so if anyone else needs it, this is a summary of what happened in that post, basically:
The dragon is his father, Semi. Gaster’s injured his right eye somehow and is screaming and Semi calls for help. They get him onto a stretcher and implied into a hospital and get him patched up, where the 3rd flashback image happens. His mom Chxlxthx is sitting with Gaster while a doctor explains that Gaster now has a small fracture on the back of his skull that isn’t going to heal--it’s much, much smaller than Gaster’s current scar, so over the duration of time between then and the present day, that fracture’s somehow grown into the crack that wraps around his entire skull. And Gaster’s thinking about all this, lying to our faces, and saying “haha, yeah, that was natural causes. Regular wear and tear. Definitely a normal thing for skeletons, probably.” ))