A lot of people that have seen horses over their lifetime think that they are gentle animals, so therefore, no problem approaching these guys, right? Well, the gruesome pamphlet you get as you enter the park will put that to rest (showing a number of bites on people.) Remember that these guys are wild animals and defend their territory! They are really pretty animals - just give them their distance...
While on the beach watch out for piles like this. You will see and smell horse bisques when on the beach so just be aware. It's not like they clean up after themselves. So be careful where you park your beach blanket.
I can think of three animals that will attack any human being without provocation: the tick, the mosquito, and the green-headed fly. They are all indigenous to Assateague Island.
Consider yourself warned.