Are you using Chrome? It is probably the NPAPI being disabled. in the address bar go to chrome://flags/#enable-npapi and then click the Enable Link.

You could do something like - before any head splits - do a world.getObjects(heads.class) and then check the size of the list - if there are too many already just forbid the split.

That is a lot better now. it is good to wait until the user presses a key to start the moving. It was hard to get started with it before since when the play button was hit you would crash before you had an idea of what to do.

you can do that, but the enemy spawning on top of you in screen transition is a drag. I have to give props for the on screen help that pops such as the movement and punch keys.