If you purchase very small grapes, you don't need to cut them in half. However, most grapes will need to be halved so they aren't too large for the salad. To easily cut grapes in half, place them on a round plastic lid (such as from a Cool-Whip container), and place another round plastic lid on top. Hold your hand over the top lid to hold the grapes in place, and hold a sharp knife horizontally to slice the grapes in half between the lids.