Choose a box that's large enough to give you a little wiggle room (assuming you're in the position to choose the box in which you'll be held captive).
Get your hands in front of you if they're bound behind your back. Push the chain down below your butt so that it is between your buttocks and your legs. Work your right leg over the chain by rotating your foot counterclockwise until you can get your entire ankle over the chain. Match the angle of your knee with the angle of your elbow to get the chain up between your thighs. Bring your left heel up and over the chain of the cuffs and then rotate your left foot clockwise until you've worked it over the chain.
Dislodge the bobby pin from its hiding place in your hair, mouth or waistband.
Remove the plastic coverings from the tips of the pin using your teeth or nails.
Insert the straight end of the bobby pin into the left-cuff keyhole if you're right-handed. Insert it into the rightcuff keyhole if you're left-handed. The keyhole of professional handcuffs is shaped like a circle with a small tab protruding from it. Stick the bobby pin into that tab.
Bend the tip of the bobby pin down using the leverage of the key hole. Then pull it out two centimeters and bend it again in the opposite direction so that you create a small "step" shape at the end of the bobby pin.
Place the first bend at the tip of the bobby pin against the tab. You should be able to feel it catch on a piece of metal inside the handcuff. Crank the pin against that piece of metal to release the lock.
Pull the bobby pin out and turn it the other direction, again placing the first bend of the bobby pin against the tab. Crank down on the bobby pin to release the ratchet and open the cuffs.