"If Bill jumps into something that relies on a lot of cymbals, I'll jump into something that relies on a lot of skin sounds; if he goes into metal tones, I'll go into wood, and so on. I basically play in his holes"

Pat Mastelotto is describing the way he and Bill team up musically. He is stating that if Bill plays something that relies heavily on cymbals, he will play something that counts on skin noises, such as drums. If Bill plays something with metal tones, he will play something with wood tones, such as a xylophone. He is basically saying that he will fill out the spaces in Bill's playing, playing the parts that Bill does not. This is a fantastic example of how two musicians can collaborate to develop a distinct and intriguing sound. By playing off of each other, they can develop something that neither of them might have created by themselves. This is a fantastic example of how two artists can collaborate to develop something really special.