Just cause I can talk about this all day, I will tell you that, should you ever be snorkeling and see a sort of stocky shark with a sawn-off-looking nose (bull shark) or one with dusky stripes (tiger shark)...swim...calmly...away...then get the hell out of the water!
For real, those are the more-lethal sharks you're likely to encounter off the U.S. (unless you're swimming or whatever up near San Francisco...not likely, as the water temp near there is usually in the 60s.) Bulls and tigers actually are responsible for nearly twice as many fatal accidents involving humans as are great whites. Although whites are migratory, and have been spotted off Florida this year.
Thanks for indulging me, all...I don't know how much further off topic we could conceivably get with this.