vary the smile width

Declare variables for the smile.
sa is the angle measured in radians.
(1 radian is a little less than 60°)

var sa = 0.25; // smile angle var dsa = 0.01; // change in smile angle

Insert a new line before calling drawSmile();

sa = sa + dsa;

Change the arc code in function drawSmile()

arc(width/2, height/2, 300, 300, sa, PI - sa);