These silencing events begin to occur after the dolphins slowly reduce the time they spend using sonar. When they are in enclosed spaces, their sonar signals bounce off walls and back towards them, which can cause psychological effects similar to those of animals who have good vision when closed in mirrors. This likely creates a self-awareness in the dolphin that can lead to vulnerability in captivity (Reiss 2000). It has been argued that when a dolphin is more aware of its presence in its surroundings, it is more susceptible to determining the difference between pleasant and unpleasant situations (Reiss 2000). In addition to self-awareness, captive dolphins also showed signs of aggressive behavior. There have been injury reports to NMFS of individuals participating in sessions with dolphins suffering broken bones, bites, bruises and even hospitalizations (Rose