Just because that's not how venom works doesn't mean that the joke therefore is bad. Humor is subject to opinion.
...you do know thats not how venom works right..you can swallow venom (though not advise) but if it kills you, its because you have cuts or ulcers.
The joke is that the VENOM the snake produces got into the food. Then, having INGESTED it, it was poison. The difference between the two is context. If it bites you and you get sick and die, it was VENOMOUS, but if you eat it and you get sick and die, it was POISONOUS
Venom is not poison