Why does the last drop of tea always run down the spout of the teapot?

Why does the last drop of tea always run down the spout of the teapot?
Joseph B. Keller, Professor Emeritus in engineering and mathematics at Stanford University, found that teapots drip not because of surface tension on the pot but because of principles of liquid flow and air pressure.

For a whimsical pseudo-explanation with wonderful illustrations click here.