From: Rabbi Moshe Sofer
To: Rabbi Chaim
The Chasam Sofer rules that a single witness — including a woman — may be believed to testify that a dangerously ill animal exhibited pirchus after shechitah. Because the animal's status as safek neveilah arises from two competing chazakos (chezkas chai versus chezkas eino zavuach) that cancel each other out rather than from a straightforward chazkas issur, the ordinary bar against accepting a single witness in the presence of chazkas issur does not apply.
Source: Shu"t Chasam Sofer YD §20