How well do you spot the spots?

Mark Twain said, "I was born modest; not all over, but in spots."

One aspect of bridge that separates the top players from others is taking full advantage of the useful spot cards (2 through 10) - in particular, knowing when a low spot is a winner.

How is that relevant in today's deal? After West leads the club king, how should South proceed in four spades? Did West have a more successful opening lead?