When a rabbit's ears stick up, it usually means that it heard or smelled something new. A rabbit tends to listen carefully to decide whether it needs to make a quick escape. With its ears sticking up, the rabbit is ready to catch the sound coming from all directions.
An acute sense of hearing helps the rabbit to stay away from predators. Rabbits are able to hear sounds from a mile away. However, this constant checking for danger can be extremely stressful for rabbits. Talking in a low tone helps to relieve stress in pet rabbits. Being picked up too often can also be a frightening experience for a rabbit.