Things you can own: Prank shark's fin

Shark Fin for Swimming, from Fin Fun

Create a frenzy at the pool with this exciting new toy. You won't believe how much fun it is to swim in. Comfortable elastic straps are adjustable to fit any size. Made from cross linked foam and high quality neoprene, the shark fin is durable, easy to swim in, and will provide many hours of fun, creative play. Straps can stretch up to 40 inch chest. We strive for high quality construction in a beautiful and functional product.

Available here