Biology can be an important model for robotics but not all robots would benefit from mimicking biological systems. Airplanes and helicopters are good examples of machines that do not benefit from mimicking birds or flying insects. Another example of machines that do not need to mimic nature are machines that have wheels. Robots with wheels may be able to move around much more efficiently than they could with biology-inspired legs, especially if they only move around on smooth, even surfaces like floors and roads. However, robots that need to traverse uneven terrain may benefit from being inspired by humans and other animals that have legs. Robots that are meant to interact with people may benefit from mimicking human biology. Mimicking human speech or human physical features may make it easier or more comfortable for people to interact with the robots.