This is a test of commonsense. Complete the next sentence:

How to fillet a mackerel
Place the fish onto a cutting board.
Fold down the pectoral fin (on the side of body) against the head.
Put the blade of your knife behind the folded fin, holding the knife at a slight angle.
Sever the head and fins from the body in one slice of the knife. When you are cutting a mackerel, do not press down with the hand holding the fish.