OMG that IS gross - and also dangerous - there's an article about a puppy mill dog - and
this is GRAPHIC SO STOP IF YOU THROW UP EASY
a woman wrote an article about a dog she rescued - her little anus was full of fly eggs that had hatched - I won't go into details but know this - it CAN happen - you may want to get a vet check in a week or so and make sure none got in there - you dont want to hear details but it was one of the worst things I ever read and saw
