Rubber Bones!

photo via answers in genesis

materials:
jar, chicken bone - a leg or "drumstick," and vinegar

how to:
1. Rinse the bone in water.
2. Feel the bone: "Like our bones, chicken bones have a mineral called calcium in them to make them hard."
3. Place the bone into a jar and cover it with vinegar. Then, put a lid on it and let it sit for 3 days.
4. Rinse off the bone and feel the texture. Try bending your bone!

explanation: 

"Vinegar is considered a mild acid, but it is strong enough to dissolve away the calcium in the bone. Once the calcium is dissolved, there is nothing to keep the bone hard - all that is left is the soft bone tissue. That's why it's important to drink milk!" via Science Bob