Well, if we were to consider the idea in a very theoretical sense within Supernatural Sam fanfiction, it would be completely against the nature of the show. Supernatural is about hunters, demons, angels, and the like. Sam is a human character with complex emotions and relationships. Incorporating bestiality would not only violate the show's core values but also be distasteful to the majority of the fan base. So, in practice, it's not something you'd find in well - written, in - character fanfiction.
The concept of bestiality has no place in Supernatural Sam fanfiction. The show is centered around themes such as family, sacrifice, and the battle between good and evil. Sam Winchester is a character who is often portrayed as a hero, a hunter, and a brother. Fanfiction about him typically explores his relationships with other human characters, his growth as a person, and his adventures in the supernatural world. Bestiality is an inappropriate and unethical concept that goes against the very essence of the Supernatural universe and its characters.
In most Supernatural Sam fanfiction, bestiality is not a common or acceptable theme. The Supernatural universe generally focuses on human relationships, the fight against the supernatural, and the bond between the characters like Sam and his brother Dean. Fanfiction writers usually adhere to the ethical and moral boundaries of the show's overall tone, so bestiality would be highly out of place and not likely to be part of a legitimate story.