Brownies and cheesecakes can be difficult to slice through and I often get asked how they can be sliced cleanly. The fact of the matter is that any sticky food can be a bit awkard when sliced, whether it is a fudgy cake or a rich custard-type pie, because the same qualities (gooey, sticky, creamy, etc) that make it so delicious also make it stick to the knife. This results in sloppy slices and a knife that has as much brownie stuck to it as the slice left in the pan. The way around it is to keep a moist paper towel or dish towel on hand and to wipe the knife clean after every slice you make. This keeps the knife from getting gummed up and, because the knife will be damp when it goes in, should keep most of the brownie/cheesecake/etc. in the pan and off the knife in the first place.