As Jolene Creighton in Quarks to Quasars puts it, “The quick and dirty way to separate venomous creatures from poisonous ones is by thinking about bites: If you bite it and die, it is poisonous; if it bites you and you die, it is venomous.” So a cobra is venomous and a poison dart frog is poisonous. (I guess if you want to be picky, a snake could be considered poisonous if you eat it and ingest its venom.)
