It’s one of the plots to the FlCL anime. https://flcl.fandom.com/wiki/Medical_Mechanica

What is explained, however, is that Medical Mechanica eventually uses the ‘iron’ factories to iron out the surfaces of the planets they are put on, as Commander Amarao puts it, “Ironing out the wrinkles in your brain so you can’t think.” This may be a reference to the fact that “smooth brains” have lower surface area and are incapable of complex thought. Only innate feature of cognitive ability remain (Koalas for instance have “smooth brains” and are unable to eat eucalyptus leaves on a plate in front of them and can only eat when plucking the leaves directly from the tree).