Webster bites Sebastian and says he's from Queimada Grande, aka Snake Island, which is in Brazil. He's a pit viper of some kind.
Though Webster doesn't too much look like examples I've seen, his homeland suggests he's a Golden Lancehead viper, which are only found on that island. Wikipedia. Smithsonian. It's a cousin to the Fer-de-Lance viper found on the mainland. According to the Smithsonian article, they evolved from the Jararaca, which some people consider synonymous with the Fer-de-Lance, but Wikipedia has a separate page and species name for it. To me, Webster's strongly zig-zagged sides make me think of the Fer-de-Lance, but 🤷🏻♀️. Well, it's got to be a Bothrops, either way. The Golden Lancehead's venomous bite is so potent that it practically melts human flesh, and a victim can be dead within an hour. No wonder Webster is shocked by Sebastian's ability to stay alive, let alone remain standing. We are talking major necrosis, kidney failure, and bleeding to death.