Yosef Karo, Shulchan Aruch — 51 The law of a needle or thorn found in a beast
“ And if it's doubtful whether it's due to illness or from a thorn or needle - it's kosher (B"Y in the name of O"M) , and see above in Siman 49. And all the more so, it's proper to rule it kosher like this when the skin and flesh are pierced through into the cavity. However if it gets pierced by a thorn in our presence and the beast is slaughtered and the thorn is found stuck in our presence from the wall of the beast to one of the parts, it would seem that it didn't pierce any other place, therefore if it meets the heart and so forth but doesn't pierce into its chamber - it's kosher. ”
