Hullin 9: Presumptions, Prohibitions, and Danger

A Torah scholar must learn 3 skills: writing, kosher slaughtering, and circumcision. And 3 additional things are subject to dispute - whether they are skills that are required or commonplace: tying the knot of tefillin, the blessing for the wedding, and tying tzitzit. Also, standards of presumption regarding an animal: while it's alive, the presumption is that it's not going to be kosher. Once it's slaughtered correctly, then the presumption is that the animal IS kosher, unless a blemish is discovered. Also, what if a wolf bite is clear on the innards of an animal - but perhaps it's a puncture after the shechitah? Or might the bite have obscured a hole that would have made the animal a treyfa? What about a snake's poison? But the wolf/intestine is a concern of a prohibition! And the snake concern is about danger, which requires greater stringency!