What is "thickens"

Usage examples of "thickens".

And the Vistula flows, and the mill mills, and the narrow-gauge railway runs, and the butter melts, and the milk thickens -- put a little sugar on top -- and the spoon stands upright, and the ferry comes over, and the sun is gone, and the sun returns, and the sea sand passes, and the sea licks sand.

Tulla, who was always shoveling about for mice in the sand, bit into things with two incisor teeth, and never wore shoes or stockings: Barefoot run the children, and the willows shake themselves, and the Vistula flows for evermore, and the sun now gone now back again, and the ferry comes or goes or lies groaning in its berth, while the milk thickens until the spoon stands upright, and slowly runs the narrow-gauge train, ringing fast on the bend.