They have poison potions, right? (I don't have pre-release)
Well, doing this:
Pork: Any food item
This would cause the item to look like food, but have the effects of the poison.
"But robo, how would you tell poison from real?"
The poisoned food would not stack with other food, and would be slightly darker. It would also have the name when moused over slightly purple, so it's not OP and the player would have a chance of recognising the poisoned food.