In this case he plays the eight, a high card, to call for the higher-ranking of the possible side suits.
West led a singleton heart, a poor choice, since it was likely to help South develop her known side suit.
Leading into the declarer's side suit would not be a normal move.
But West made an inspired lead of the diamond eight, finding the only side suit in which his partner held a top honor.
A 5-3 side suit will produce at most five tricks.
He made his contract, losing a trick in each side suit.
The answer, he decided, was that West held an honor in each of the side suits and did not have a passive lead available.
By agreement, a bid of a short side suit after a single raise, hoping to reach game.
Clearly he had no losers in the side suits.
The defense has enough entries that it will be able to continue leading the side suit.