Hey, I'm not looking for anything that could be marketed. I'm just looking for ideas a 4th grader could use in a class where an invention is expected. It has to be something that can be constructed and actually used. My idea is a "finicky cat feeder." You put a bended piece of plexiglass (in a tunnel shape) onto a sheet of plywood. You cut holes into the plexiglass where food can be dropped and allow the cat to stalk pieces of food along a path. Any cat owner knows a cat eats better when it stalks its food.
Something along that line.