The animation that controls the height uses different
animation curves depending on its direction.
When the animation moves forward, it needs to quickly make 
space for the speech bubbles. For this reason,
the forward curve runs the entire height animation within
the first 40% of the overall appearance animation.
When the animation reverses, it needs to give the speech bubbles
enough time to disappear before contracting the height. 
An ease-out curve that uses all the available time is a
good way to accomplish this behavior.

Animate the speech bubbles

The typing indicator displays three speech bubbles.
The first two bubbles are small and round. The third
bubble is oblong and contains a few flashing circles. 
These bubbles are staggered in position from the lower
left of the available space.