Books
It’s all right, it’s just a horse in the bathroom.
— Douglas Adams ‧ Dirk Gently's Holistic Detective Agency

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
An absurdly calm reassurance about something wildly out of place. Calling a horse in the bathroom "just" that plays down the strangeness so much that it becomes funny. The comedy comes from the mismatch between the reassuring tone and how bizarre the situation really is.
Context reviewed