Game Help:Sims 3 Tomb Holes
From SimsWiki
No your sims arm wont come off neither will they be hurt there will simply only be bugs crawling out of the hole r other insects yur sims will get scared and takeout their hand and wait for all the bugs to go away before putting their arm back in the hole.
holes can cotain anicent coins,relices, or other small objects to use a hole all you needto do is click on on and then click inspect