i saw a mouse with an X-shaped battery compartment. first thought: this is stupid - who designed it? 5 seconds later: oh. 10 seconds later: OHHH! the X slot fits an AA or an AAA battery - whichever you've got lying around. the part most people miss is that the shape also makes it physically impossible to load both at once. there is no warning label, no instructions and no way to screw it up. the geometry does the thinking for you. japanese has a word for this. poka-yoke = "mistake-proofing." the product refuses your stupidity before you can offer it. i wish more things worked like this.