Unlike R's movement which is calculated a spot at a time, B's movement is calculated when a spot is tapped. In general, if the spot cannot be reached, a red 'x' appears, if it can be reached a bubble appears and B sets in motion towards it, and if there is no B, nothing appears. Well, we have found that the first two conditions do not always hold true. There are in fact several ways to manipulate B's movement, which can be broken down into three general categories: 1. Send B to a spot that has a block overhead; 2. Set B on a path and then alter the path on him; 3. Make combinations of taps such that B is tricked into going elsewhere. As a community we have adopted names for these three as follows: 1. Low Ceiling effect (also known as Claustrophobia); 2. Autopilot exploits; and 3. Inertia-based bugs. Please see the respective pages to learn more.