Brian Kahrs once went swimming at Manasota Key beach in Florida, and noticed many shark teeth in the sand. He went back to the beach and recorded this video, where he counts how many shark teeth he can find over the course of three hours.Online sources like this local hotel website and this fossil enthusiast website indicate that the dark-coloured teeth found on the beaches in the region are fossilized teeth dating from prehistoric eras. Credit: Brian Edward Kahrs via Storyful