I'll bet they're discarded plastics.
I agree with the idea that those may be discarded or lost plastics. We've found them from time to time from people either being careless or downright irresponsible. I've wondered, too what happens to plastics that are pinned to a snag.
I've never lost a lure inside a bass or a crappie, though I've had bluegills suck a small jig off the hook.
Jerry - You ought to send those photos to BASS. I think they would find that very interesting. Personally, I'd like to see them work with the In-Fisherman publisher to print the I-F illustrations on properly removing a lure from a deeply hooked fish. We've used that method to relase any number of small crappie. - Roberta
"Anglers are born honest,
but they get over it." - Ed Zern