Justin E. H. Smith in his Substack Newsletter:
Among the many rules for the conduct of life that Pythagoras passed down to members of his philosophical cult, there is a peculiar prohibition that keeps coming up in late-antique testimonia: Consume no lentils. Decline all lupins. Eat not pulses. Abstain from beans. Different authors provide different rationales for this (Diogenes Laërtius says that it is because beans resemble testicles, and perhaps also the gates of Hades), but we may isolate three of them as the most common and most compelling. First, you must not eat beans because they produce within you an undesirable flatus, damaging to your health and noxious to those around you. Second, you must not eat beans for the same reason you must not eat meat — they too are ensouled, and may well harbour the particular souls of your reincarnated love ones.
If I may pause here for a moment before getting to the third reason, allow me to note that the first two are not as different from one another as you might suppose: when in the Meditations of 1641 René Descartes found it important to deny of his own soul that it is a “subtle vapour”, he was going against a very deeply ingrained strain of popular philosophy, extending back well before the golden age of classical Greece, according to which the vital principle in a body is itself a sort of flatus.