You are in a group of people who are gathered with some random items of food. Someone searches out a knife to cut a quiche so it can be shared out. Some time later, you would like to divide a chunk of cake in a similar manner. Course of action:
Search out another knife (or possibly other implement) to cut the cake.
Wash the existing knife and cut the cake with it.
Attempt to wipe or scrape as much of the cheesy goo as possible from the knife before cutting the cake with it.
Lick the knife (careful, it's sharp!) so you can cut the cake.
Pick the knife up, pretend you can't see the wodges of quiche stuck to it and just cut the cake with it anyway.