Avatars have become a fundamental part of collaborative virtual environments. They are the visual embodiment of the user and are designed to address key issues in the interaction process between the user and the CVE. Giving avatars expressive abilities has been considered essential in computer human reaction. Having an avatar, which has the ability to express facial expressions, as a part of the computer interface increases human performance. Researches have provided strong evidence that emotions can be effectively portrayed visually in avatars to represent human users in collaborative virtual environments. These include manipulation of facial expressions as they are efficient carriers of emotions. However, avatars have still only limited variations in their emotional expressions to become believable entities.