A knife has a first head and a second head. The first head has a first pair of arms and a first pair of knife edges. Each arm of the first pair of arms hangs over a different knife edge of the first pair of knife edges. Similarly, a second head has a second pair of arms and a second pair of knife edges. Each arm of the second pair of arms hangs over a different knife edge of the second pair of knife edges. The first head is connected to the second head.