S9·E12 Sharp Teeth

Episode recap

Topic: Supernatural S9E12 (Sharp Teeth) episode recap.
Constraints:
Use ONLY verifiable facts from the provided SYNOPSIS and SOURCES.
No invented titles, names, dates, counts, awards, ratings, box-office, or plot points.
If a detail is not in the material, omit it.
Style: Original, neutral, encyclopedic prose, plain text.
No markdown (no asterisks, no headings, no bullet points).
Word count: 280-380 words.
TMDB Episode Synopsis: Six months after his disappearance, Garth turns up injured in a hospital. Sam and Dean arrive separately to investigate and soon discover that their friend has undergone a startling transformation.
Source [1]: Series title Supernatural (2005). Genre: Drama, Mystery, Sci-Fi & Fantasy. Tagline: Saving people, hunting things, the family business.
Source [2]: Created by Eric Kripke. Broadcast on The WB and later The CW. 15 seasons. September 13, 2005, to November 19, 2020. Sam (Jared Padalecki) and Dean (Jensen Ackles) hunt demons.
Source [3]: Created by Eric Kripke. Cast: Jared Padalecki, Jensen Ackles, Jim Beaver, Misha Collins. Brothers follow father's footsteps as hunters, fighting monsters, demons, and gods.
Source [4]: (Slovak site) General commentary, not useful for specific episode facts.
Source [5]: (Netflix) Availability info, not useful for episode facts.
Episode: S9E12 (Sharp Teeth).
Plot: Garth (friend of Sam and Dean) reappears in a hospital six months after disappearing. He is injured. Sam and Dean arrive separately to investigate. They discover Garth has undergone a startling transformation.
Context: Sam and Dean Winchester are brothers who hunt supernatural beings like monsters, demons, and gods.
The provided synopsis is extremely brief (only about 40 words).
The instructions say: "If the synopsis is sparse, stay concise rather than guessing."
The instructions also say: "Write a grounded 280-380 word episode recap."
Conflict Check: If I only use the provided facts, I cannot reach 280-380 words without inventing details. The synopsis only contains: Garth's disappearance (6 months ago), Garth's injury in a hospital, Sam and Dean's separate arrival to investigate, and Garth's startling transformation.
Constraint Priority: "You write ONLY verifiable facts that are explicitly supported by the provided SYNOPSIS and SOURCES. You