...went to a restaurant.
Waiter arrives to take their orders.
1st pig has a starter, 2nd pig has a starter, 3rd pig has a glass of water.
Main course arrives. 1st pig has a main meal, 2nd pig has a main meal and 3rd pig has a glass of water.
Dessert arrives. 1st pig has dessert, 2nd pig has dessert, 3rd pig has a glass of water.
On the way home, the 1st pig asks 3rd pig, "why did you only have glasses of water, while we ate?"
3rd pig smiles and says "well, one of us has to go wee, wee, wee all the way home".