The fin doesn't look all that real, but if I'm in that situation, I'm fairly certain the "realness" look of the fin is way down the list of things I'm thinking of at that moment. I'm not sure what I'm more afraid of..being caught on camera panicking, or actually being that close to a shark in the water. This is done by a comedy group Just For Laughs Gags. The string section seemingly beckoning the shark is a nice touch.