Josh took Helen into the bedroom without the others knowing, and told her how to play the game.
Then, when the others were all together, he asked them to pick an object while Helen was in the bedroom.
They called Helen back in, and Josh pointed at a few items and asked Helen if it was the item that the group picked. Helen got it right everytime, but the others didn't know how.
They each thought that they had worked it out, but when they tried they got it wrong. It took about an hour and a half until they finally got it (they were given a lot of clues).
The secret to the game was that when Josh named (or pointed to) a BLACK item, the NEXT item was the correct one.