Pass me the scalpel, I'll make an incision
I'll cut off the part of your brain that does the bitchin'

from Beastie Boys – Make Some Noise Lyrics on Rap Genius

Formaldehyde is used as an embalming agent to preserve organs. MCA will remove the offensive part of your brain and preserve it for posterity, so that you can always see what you used to be like.

Props to Shriekin_Wizard for contributing to this explanation, even though the people inside the intewebs declined to give credit. Sadly, they do that sometimes…

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