Bath Bomb

I got what I thought were some bath bombs for Christmas, and I've been trying them out.  But they were not what I was expecting.  By their very name - bombs - I thought they would explode and fizz up a lot more, have a bit more of a violent reaction with the water.  But that isn't the case - they just kind of slowly melt away.  Indeed, in the last bath I had there was some bath bomb left behind when I emptied the tub - brown in color, so it kind of looked like I had done something unpleasant in the tub.  So I have my doubts whether these are indeed bath bombs.  They seem to be more like some kind of bath salt or soap.  But a quick internet search suggests that bath bombs can expire.  Have mine already expired, even though it is not that long after Christmas?  That would be disappointing.