Yosef Karo

“ Some say in these times when are not expert in performing checks it can be ruled treif if the needle pierced it from both sides even if no blood clot is found and no rust, for we do not rely on this, on our checking, once it's been pierced from both sides (A"Z and O"H) and that's the practice. A needle or thorn that's found in the Hemses or Beit haKosot inside it or stuck in them, the rule is it's kosher in all regards and needs no checking (H"M) . ”

“ Rema:These are some who forbid it in the Hemses even without a through puncture (Tur in the name of Rashi, U"T l.v. and T"H #165) . 8 If there's found in one of them, submerged a needle or thorn but it's not pierced from one side to the other, we turn it inside out and check it from outside. If there's found on it a blood clot it's definitely pierced through and it's treif, otherwise it's kosher (Tos., H"M p. 6 in the name of Samak, and all the poskim) (even if there's only a little bit of the external peel that's not pierce) (see the previous siman, #21) . ”