Robin as a manatee (becoming a mermaid) to Marshall.
- For the episode revolving around this theory, see The Mermaid Theory.
The Mermaid Theory is the theory that a man will eventually want to sleep with any woman after a period of time, no matter how initially repugnant. The only way that a woman who will become unattractive again is pregnancy and becoming mermaid again is possible by breastfeeding.