It looked like a cut from a blade, it was a super clean cut. I haven't found a breeder yet, but I haven't really been looking that hard. I guess this'll jump-start my search for a local breeder since I don't have enough snakes to buy in bulk and shipping always seems to cost as much or more than the feeders themselves. Definitely won't be able to breed feeders myself where I'm living now, even if I do get permission for more snakes.

As for how I thawed, it was about 30 minutes in cool water until squishy all the way through the belly and chest. There weren't any problems with the others in the box which is why I wasn't expecting to find one almost without a head.