Also, could use a bigger change in color or other indicator of which tool you have selected - depending on the lighting you're playing in, it can be hard to tell at a glance which one is active.
Not a bad little time-waster while waiting for other things to load. Good physics, though I agree with the earlier comment that this almost seems like an exercise for a fuller game.
A bit laggy, but overall good. I like that the upgrades are something you actually have to train rather than just buying stuff and slapping it on the dog