From: Rabbi Moshe Sofer
To: Rabbi Meir
The Chasam Sofer resolves an apparent contradiction in the Tur (YD 33) between the positions of the Ba'al Ha'Itur and the Rosh by distinguishing between wide and thin venom marks, or by limiting the concern about slaughter at the derusah site to cases of definite derusah only. He rules that for definite derusah in a behemah or doubtful derusah in a bird, post-slaughter inspection cannot be relied upon, but for doubtful derusah in a behemah, one who rules leniently permitting internal inspection has acted correctly.
Source: Shu"t Chasam Sofer YD §27