Responsa for Chullin 107:21

ולא ידענא ליה

R'Johanan, however, said: He should compare it.<span class="x" onmousemove="('comment',' Lit., 'he should bring and compare'. I.e., he should make another cut in this same windpipe, and if the cuts resemble each other the animal would be trefah, for it is evident that just as the second cut so the first cut too was made in an organ that had already been torn loose.');">⁹</span>

Shut min haShamayim