"There are, of course, other life forms that do their 'thinking' with parts other than brains, but these tend to be sponges, scallops and..."

"... the slime mold that re-created a map of the Tokyo subway system — not exactly a desirable cohort in which the president has placed himself. Or perhaps [Trump] is claiming to be an evolutionary throwback. Anthropologists’ 'expensive-tissue hypothesis' posits that as animals’ guts got smaller, their brains got bigger. If Trump’s gut remains so prominent, might his brain be smaller than his hands? But Trump isn’t wrong to say his belly has brains. Researchers have found that bacteria in the gut send signals to the mind about what to eat, for example. I undertook a gut check on Trump with Braden Kuo, a director of the Center for Neurointestinal Health at Massachusetts General Hospital, and he told me the large number of neurons and neurotransmitters in the gut make it a sort of 'second brain.' This is why people eat comfort food when sad or get butterflies when anxious. 'A lot of our emotions, how we feel things, comes from nerve endings in our gut,' he says.... Bandy X. Lee, the Yale University psychiatrist who has sounded the alarm about the president’s mental functioning, thinks Trump’s preference for his gut is a rare moment of self-awareness. When Trump talks about his gut, she says, he’s really referring to his 'primitive brain' — from which a rush of emotion is 'overcoming him so he’s not able to access his actual intellect.'"

Dana Milbank endeavors to digest Trump's many reference to his "gut," in "Does Trump’s great gut mean a tiny brain?" (WaPo). This isn't about the size of his belly, but about his rhetoric — stuff like "They’re making a mistake... because I have a gut, and my gut tells me more sometimes than anybody else’s brain can ever tell me" and "I know it better than anybody knows it, and my gut has always been right."