On the other hand, if you have a few quid / bucks / whatever down the back of your sofa and you're stucks for ideas on what to do with them, it's well worth investing in the full version of BTTF, available from the Hungry Software store.
See the instructions for installing Ducks data files if you need to know how you get either file - that is, the demo or the full version - to work with your copy of Ducks.