It depends where you got it from. If it raised properly, and not be some fucking twat giving it tap water, it should be fine. Hissing noise is normal, so the brown discharge we can see in the water. As a rule of thumb, give it an hour to boil for every pound it weighs. This looks like a three or four pounder, but could be hard to tell. There's not real etiquette for eating it. Some people swear by squeezing it's innards gently till it's basically mush inside, and and then just sucking all the goodness out of its hole. Did you get it from a local farmer or is it a Hentons?