You will need:
1. Soak the bones in vinegar for at least a day. Really, the longer the better for this experiment.
2. Leave the bone until it is soft and bendable - you can even tie it in knots.
3. If you take the bones out of the vinegar and leave them overnight they will harden in the position you left them, by reabsorbing carbon from the carbon dioxide in the air.
Vinegar is acidic and bones are made of roughly 10 per cent calcium carbonate. Calcium carbonate forms a framework on which bone growth takes place. As the bone soaks, the calcium carbonate reacts with the acid vinegar, producing carbon dioxide gas (this is the bubbles coming off the bone).