Hi Jay, thanks man we really appreciate it. That's a good point, and you're not the first person to get stuck on that. There is a controls option, which explains that RMB lets you expand the brush to access more biomes, but you have to use the arrow keys or WASD to navigate the menu. Pressing LMB was one of the last things I implemented, as a way of letting people just start the game by pressing LMB instead of E or enter. As of yet, mouse movement doesn't affect the menu selection. Thanks for checking us out!