To do Wacky Jacks, start standing tall and place your hands either behind your head or up just to the sides of your head. Bend your right knee up and out to the side as you crunch your upper body to the side, dropping your right elbow toward your right knee.
Then jump and switch, bending your left knee up and out to the side as you crunch your left elbow down toward your left knee.
Quickly jump and switch to the other side. Go back and forth between the sides as quickly as you can, crunching your elbow down to your knee as you raise your knee up as high as you can.