Scarecrow is a mockup of the Mars Science Laboratory (Curiosity) rover that weighs the same on Earth as Curiosity does on Mars. It is used to do Earth testing to simulate the Mars rover's drive performance. In preparation for the Mars 2020 rover mission, Scarecrow has been upgraded with a brain(!), a mast, and a pair of navigation cameras to allow engineers to test new drive capabilities for the new rover. This test build is capable of processing images taken for visual odometry while driving (that is, without stopping), drastically reducing the wait times between drive steps and dramatically speeding the rover's progress.