"If it looks like a duck" - when the kashrus of a species is called into question
Kolel L'horaah Ma'asis Crown Heights - Shiur 27 on halachic topics - by Rabbi Shraga Dovid Homnick, Sgan Rosh Kolel, on kashrus questions concerning a species itself and the reasons they arise, the Tzemach Tzedek on geese, Rav Shlomo Amar on buffalo, and more
https://www.youtube.com/watch?v=u1L8jncuTU8