How can you tell if a frozen pinkie has gone bad?

So...i usually buy my pinkies from petsmartor petco but realized feed stores have them too...and for a lil more reasonable price...i bought some a few days ago and when i went to thaw one just now it looked a lil weird to me... i cant really describe it but im worried about feeding it to my snake....so how can you tell if a pinkie has gone bad? can it go bad if its been frozen? and what will happen if my snake eats a bad pinkie?