It's the mixing of milchig and fleishig.
Milk represents birth and life sustenance. The flesh stands for corruption and death.
McDonald's founder Ray Kroc mentions running into a Florida health ordinance that prohibited milkshakes and hamburgers from being prepared in the same room. In order to pass inspection, they ended up having to put the Mixmaster in a plexiglas 'booth'.
That upset Ray's carefully planned 'service ballet' that he was so proud of.
Interesting post!
I can learn something in these threads! ;^)