No neck plug? D:

[Baby Sugarberry]

I had something similar happen with a G1 Sky Flier.  Tried to pry her head off and the neck ring stayed inside.  My personal theory has to do with a flaw in how the pony's head was made - rotational casting I believe? In any case, sometimes the plastic isn't evenly distributed in the mould and the strength of the glue far outweighs that of the thin edge between head and neck ring.  Attempting to pry off the head or cut it off separates the two, leaving the ring in the body cavity (may not be very obvious due to thin top edge). 

[CrystalCrown]

i have at least 17 g1's right now and none were like that!

could it just be something from the factory? or maybe the sweetheart sisters were just made like that? (idk because i dont own a sweetheart sisters yet)

[Baby Sugarberry]

If you only have a handful, odds are you won't see one like this. I've unglued hundreds of ponies, and so far I've had just one with this issue. It's not common by any means.  It's not an issue with SHS specifically.