Bad bag of food?

[Bogertophis]

It's entirely possible that they're spoiled, especially if your "supplier" isn't the one who actually raises the animals, but just buys from elsewhere & re-sells them. I can remember a "supplier" who did that (years back) & apparently they received a huge block of frozen rodents, and to re-sell them, they had to thaw them to separate them, & then re-freeze them. That allowed for spoilage, & your snakes will know the difference- most will refuse to eat them, but even if they do, they may also get sick.

Other reasons snakes may reject prey has nothing to do with "spoilage" but that the rodents were improperly fed something which gave them an "off" odor. It's impossible to say what harm has come to snakes eating tainted or spoiled prey- only that it's thought to have occurred somewhat rarely, & unfortunately never proven.

Bottom line- your snakes probably "know" if they're bad. Remember that the rodents are whole animals, with a whole gut full of bacteria (it's called a GI tract ) so when allowed to sit at temperatures that allow the bacteria to grow (keep in mind that freezing doesn't kill bacteria, just keeps it in "pause") they spoil very efficiently, & since our snakes eat raw food, well...it's gross.

That's also why it's recommended that you don't thaw prey by just letting it sit out on the counter, as many still do: it's too slow & allows more spoilage. Even if you do that successfully with the steak you cook for yourself for dinner, remember that's not a "whole animal" (with a heavily contaminated GI tract) AND that you also cook it, which destroys most of the bacteria. So the best way to thaw your snake's frozen rodents is either in cold water until soft (the fastest way) or in the refrigerator (the very slow way).