Cutting Brownies

We baked a few pans of goodies on Friday for A.'s new apartment open house on Sat. We like to make a double batch of brownies and put them into a jelly roll pan for bars. Seem like they always goop up and tear when we cut them. Mother-in-law taught me to use a plastic knife for cutting brownies, and to do it when they are still warm. Then they cut beautifully. No tearing edges with the knife! This I needed to know!