The Detector - Sheep is a block from the Railcraft mod. This block is meant to output a Redstone signal based on the type of Minecart that passes in front of it. The Detector - Sheep will output a Redstone signal if if a Minecart being ridden by a Sheep with enough Wool to be sheared is in front of it. The color of Sheep required to create a Redstone signal can be chosen by placing that color Wool in the Filter section of the GUI. They can be placed under or beside Minecart Tracks, and will output a signal to the side that has a small square. When a Redstone signal is active this square will turn red.