Stiff bones aren't nearly as fun as wobbly ones.
We saw an experiment where a chicken bone was placed inside of vinegar for a week. During that time, apparently the vinegar dissolved the calcium in the bone. Without that calcium the bone became flexible and wobbly. How cool is that!
We didn't have a chicken bone but we had a beef rib bone. We searched to see if this would work but didn't have any luck finding out. So we did our own experiment! After one week, we took out the bone to see if it felt any different. It did not. It was still as stiff as when we started. We'll try again with a chicken bone.