Someone very, very close to me -- someone with an IDENTICAL genetic pattern, in fact -- once made (instant) mashed potatoes and wanted to put creamed tuna on them. So some milk and margarine into a pan, add the tuna (and oil), heat, add some flour and stir like made until it thickens.
If it's not thick enough, add more flour. If you add enough flour it doesn't pour, so you add milk to thin it.
When the proportions of milk and flour are correct, pour it on the mashed and eat.
Something in this recipe makes the oil cause scours.
You also end up with a LOT of creamed tuna...a lot!