Swiss cheese has holes in it because of bacteria passing gas.
But actually it's the work of armies of microbes, specifically Propionibacteria shermanii. It's a beautiful, natural process, with the advantage that it enables cheese makers to charge good money for a product that by law is partly air. It seems Swiss cheese with big holes fouls up modern slicing machinery. For many it just won't be the same. Come over to my house, bud, and I'll sell you some cheese that's all holes.