The pianos do begin to bleed, and House will be able to collect a sample to take back, although occasionally, when the blood glints in the light, there are hints of static. When examined under a microscope, it doesn't appear as if there are specks in this blood. Or anything, actually. It doesn't seem like blood. It doesn't even seem like water, because water would have something show up under a microscope. It's like looking at a blank microscope slide, except tinted red.