Fold a paper in half. Cut a line in the middle using a craft scissor.
Fold each flaps to make 2 triangles.
Unfold them.
Open the card.
Push the triangles up and pinch the edges.
Close the card and push down the folds to make them well-creased.
Open it back and draw a shark on it. Cut along the line.
Glue the outline but do not glue near the mouth or the card won't open. Paste it on another piece of paper; preferable of different colour.