App user is given several lens options to choose from to animate his/her face.

Video or picture format
Facial expression function available with app update as of September 15, 2015 according to official Snapchat blog.
Lens change daily, they appear again sporadically, some animations include cartoon eyes, fumes exhuming from the nostrils as if to give a stressed or angry emotion, the appearance of broken or shattered glass, heart eyes, floating hearts some more comical animations include crumbs coming out the mouth with cheeks looking bigger than normal or a rainbow river coming out the mouth making the eyes larger in size.
Each lens comes with a little caption instructing the user to make a specific facial expression, such as raise your eyebrows, to play along with the animation.
Snapchat has been available for several years with great changes and improvements that users have excitedly embraced, which has made Snapchat one of the most popular apps among social media networking.