unknown cause of death

[pteropod]

awhile ago one of my grove snails died in a very strange way that ive never seen before and i want to know if anyone has any idea of what could've caused this. its body was completely out of its shell and both of its eyestalks were missing. one of the eyestalks was next to the snail which makes me think it mightve fallen off by itself. it was only housed with two other grove snails and one milk snail so its unlikely that it was attacked. it was also making a strange expression with its mouth open and brown lines were inside of it. its head was also misshapen.

all the other snails in the terraium have been doing fine. though im still worried about what could've caused this and want to find out what happened so i can hopefully prevent something like this from happening again in the future.

pictures to get a better understanding of its condition:

postimg.cc/gallery/CqYBLYy