Searched but didn't see this, but apparently inert does not mean what it used to:

http://www.nbcdfw.com/news/local/ATF-Investigate-Explosion-in-Grand-Prairie-Home-256793491.html

Curious what it was. It didn't kill him, so either it was a near-dud or something tiny.

No mention of the family dog getting shot.

We have had several accidents over the years with "INERT" ordnance item. We used to send EOD Techs to the EOD School every few years to 'Recertify' all of the Inert training aids and there were always a few items that were found to still contain some energetic materials.

This was probably a case where the main charge was removed but the detonator was still live. Even the smallest items (about 1 oz. of H.E.) will kill or maim if detonated within a meter or so.