I bet anise (star anise?) or ... what's that other spice...I have some in my spice cabinet. It's a seed of some sort but not the above one. Either way, I bet a hint of that would be nice in a stout! It'd probably mortal and pestel it up just a bit to crack it and throw it in dry-hop style, maybe with a tad in at 20 mins remaining on boil actually.
Could be good!