[drache]

that pic looks familiar
wasn't that in some other thread?
the dark belly indicates blood pooling in the rodent's belly, because cf cellular breakdown
I don't know for sure that this only happens when the rodent is defrosted and re-frozen
in and of itself it's not harmful
even if a rodent was defrosted and re-frozen, it's still okay
in my experience, if a rodent has been defrosted for too long before it was re-frozen, or re-frozen multiple times, it also goes through other colour changes, but since I've not had it happen a lot, my experience is limited, and I could be wrong
in any case
I have fed rodents looking like the one in the pic with no ill effect