it's some sort of spongy, raw pasta-like stuff based on the descriptions. no legs, no bones, no feathers, looks like nothing as far as animals are concerned. the hungarian guy who spotted these said that from the inside they have a light cream color that becomes greyish when exposed to air. the hungarian journalist did some research and he's saying that according to some canadian experts it's not even organic. looks like some chemical material to me, a bit like those insulating foams you use for construction that didn't properly dry and harden after usage
or like the hungarian article and
@icemaη speculate: just *aliens*