Do commercially frozen quail require particular prep before cooking?

The author slow-cooked frozen whole quail from a supermarket, resulting in tender meat, but two of the quail exuded a mysterious, dark, pasty substance. This unknown material was brown, smeared easily, and resembled feces, causing the author to discard the contaminated meat. To prevent this in the future, the author seeks to identify the source of the paste. Possible explanations include coagulated blood, liquefied organs, or actual bird droppings. The author suspects that cleaning the quail cavities beforehand might prevent this, especially if the paste originated from organs or feces. They are unsure how to effectively clean the cavities of quail without spatchcocking them. The author wants to determine if pre-cooking preparation would have prevented the issue. Previous attempts with similar cooking methods have not resulted in this outcome. They seek advice on proper quail preparation to avoid this unappetizing issue.