Hollow vessel blows up

The other day I was turning a piece of mystery wood that I had high hopes for.  I was holing away and managed to get it where I wanted and shifted my attention back to the outside of the vessel.  As I has shaving away at it there was a bang and a little recoil in the tool.  Turned off the lathe and found a knot had decided to liberate itself from the rest of the piece.

Yes, I might have been able to salvage it in someway, but was kind of disgusted with it by now. Decided that it might make a good birdhouse.  We regularly have some small birds set up residence in the space between the sheet rock and roof in our garage.  They enter through vent holes.  I went ahead and cut a hole where the knot blew out after shaving down what would now be the top of the house.  

The new birdhouse