In the rule “The Night” (2.3), insert a step into the atomic action “Sale”, after “They buy their meal” and before “They leave the plaza”:

They eat their meal: If the Active Customer’s Choice contains the Ingredient “Oyster”, then the Yard roles a DICE20 to determine the outcome(s). (If multiple conditions apply, then all of the applicable actions must be followed in the order they are written.)
* If the result is equal to 1: The Active Customer shares their story on social media. During the next Night, that Truck does not perform a Sale.
* If the result is less than or equal to 2: The Active Customer gets food poisoning. The Truck whose Menu contained the purchased Dish refunds the Price of the Dish by deducting the Price of the Dish from that Truck’s Dollars (to a minimum of $0). The Active Customer returns home and is immediately removed from the Customers list.
* If the result is greater than 15: The Active Customer is pleased, and gives a flat Tip of $5, which is immediately added to that Truck’s Dollars.
* If the result is equal to 20: The Active Customer shares their story on social media. During the next Night, that Truck gains an additional $5 from any Sales that they perform (on top of the Price of the Choice and any Tips).

If the proposal “No Such Thing As A Free Lunch” has been enacted, in the subrule “Dishes” (2.1.1), replace the paragraph starting with “The available Ingredients” with:

The available Ingredients and their Costs are: Oyster ($5), Beef ($3), Lamb ($3), Chicken ($2), Pork ($2), Falafel ($1), Wrap ($1), Salad ($1), Cheese ($1), Sauce ($1).

Otherwise, if the proposal “No Such Thing As A Free Lunch” has not been enacted, replace that paragraph with:

The available Ingredients are: Oyster, Beef, Chicken, Lamb, Pork, Falafel, Wrap, Salad, Cheese, Sauce.