Sharks have tiny pores all over their snouts, the better to detect the slightest muscle twitch or heartbeat. Experts suggest that to avoid a shark attack, don't swim after twilight, don't swim with an open wound (sharks can smell blood three miles away), stay close to shore and don't wear shiny jewelry, as the shimmering can sometimes be mistaken for fish scales. You don't want the shark to think you're a fish!