If it is animal, you can eat it. If it is tough, get it into small enough pieces and then do as the Inuit (Stephanson, Fat of the Land) did- roll around in your mouth a few times for flavor and then just swallow it.
Does anyone have a link to nutrition data for gristle(a.k.a animal connective tissue)? I have searched the net and sites have only said to 'trim off the fat'---not very useful advice. I hope the PALEOS can enlighten me on this issue...