Imagine a warehouse with several vertical stacks of crates. Standing on top of one of the stacks, James Bond has to reach a particular crate. He can't touch the electrified warehouse floor, so he must topple some of the stacks to reach others to eventually get to the target crate. His problem, then, is to figure out the right stacks to tip over in the right directions in the right order. A stack falls as a unit, crates can tip over only into empty spaces, and Bond can't leap across empty space or move diagonally to reach other crates.