Bit 2 means a moving weight. This is used for, among other things, determining where to flip objects in or out. The top bits contain, where applicable, information about when the player was last standing on that tile, and in which direction he left. If the player has been on an amoeba's tile less than approximately 5 seconds ago and a random number falls within a specific range, the amoeba will follow this trace. The higher the level, the more likely this is to happen, and the more intelligent the amoebas will appear.
Amoebas can also change directions if they find a clear, horizontal or vertical path to the player.
This too is more likely to happen on higher levels.