Lay an empty toilet paper roll on a flat surface. Press on the toilet paper roll to flatten it.
Draw a triangle at the top of the toilet paper roll using a marker; the point of the triangle should end about 3/4 down the roll. Draw two triangle shapes on either side of the back of the roll opposite one another; the points of these triangles should almost meet.
Cut the triangles that you have drawn out of the toilet paper roll. The triangle at the front of the tube will serve as the shark's mouth and the two other triangles create the back and tail of the shark. Set the piece of the roll removed from the shark's mouth aside.
Glue the piece of tube removed from the shark's mouth to the top center of the tube, creating the shark's dorsal fin.
Draw 12 small triangles on white construction paper with a marker. Cut out the triangles. Glue three triangles to the top and bottom of one side of the shark's mouth, and glue three triangles to the top and bottom of the other side of the shark's mouth -- these will serve as the shark's teeth.
Paint the shark with blue or gray paint. Use black paint to add gills. Glue a googly eye to either side of the shark, just above the tip of the triangle that forms the shark's mouth.