The fly brain is found in chests in the underground jungle. It is an accessory, that, in singleplayer, slows down the physics of the game to 1/4 of the regular speed. It can be combined with bee wings to create fly wings, which look the same, but have halteres. It works like bee wings, but slows things down. Fly wings can be combined with a gold/platinum watch, to create time wings. These are like fly wings, but are lighter and emit glowing white particles, and they do not slow the player, only the surroundings. It will stack with the fly brain, making you slow, but everything else even slower.