Sound effects artists are known as Foley Artists. I did a quick google search on Foley artist and found a few sites with info including Wikipedia that had an example of a bone snapping using a stick of celery.
Wikipedia - Foley artist. Depending how loud or if he can use a mic will depend on what you use, maybe a stick breaking would make a louder "bone" crack than celery in this instance. Found this idea for a squishy sound at another site "'Flubber' (they sell it in toy stores) is great for wet swuishy sounds; so is gelatin and liquid hand soap." There were also links within Wikipedia to other sound effect sites, so have a look around and I'm sure you'll find something.
When was the last time you did something for the first time? 
