Believe it or not, you can really work your biceps without any weights at all. There are two methods to "No Weights curls\"". Thumbs Up is where you bring your upper arms 45 degrees from the upper body and with straight arms clench the fists really tight and as you slowly move your forearms towards your shoulders rotate your wrists so the thumbs are facing each other. "
At the top of the exercise, squeeze with all your might for queen and country. If it ain't hurting you're not squeezing hard enough. When the pain is unbearable, without moving your elbows unwind the arms back to the starting position and start again.
As there are No Weights, it is really important to squeeze all of the way up and all of the way down. If you find this difficult, then squash some paper into a ball and squeeze that as hard as you can. Still finding it difficult? Add more paper.