We just got a baby cavy a month ago for our daughters birthday. He is starting to put on alot of weight, in fact he is quite round. I recently noticed a "thick" area behind his head, between his ears on his neck. I worry about an abcess or something from hay but, because of his recent weight gain, I didn't know if it could just be fat storage or if they just naturally thick around the neck. I don't exactly have another one to compare it to so I hope you guys can help me. I'm trying my best but still in the dark. Thank you.