@Eva,
They are not strictly onion rings.
They are fat rings which is the reason they are so good to eat.
As you bite into them with your mastication kit, natural or moulded from plastic, with gold inserts for the pirates, and grind them up prior to transferring them by a series of muscular wriggles, which I know there's a word for but I feel it impolite to use it before a well brought up non-scientific audience ( it's horrible ) into the eosophagus and along it into the stomach, which only has only one compartment to prevent us chewing the cud for otherwise we would philosophise too much and nothing would ever get done, or regurgitating the food for our young, which doesn't bear thinking about from a tit-man's point of view, and thence 0n a progress through the descending, transversing and ascending colons, and into a system of colons with less ridiculous names, the ileum, the jejunum, bypassing the appendix most of the time, and the sigmoid (is this a Freudian joke spendi? Ed.) from whence to the rectum, the bulk of the liquid from the pre-dinner drinks, and the soup, being drained off into the bladder, where, in both, there is a build up to avoid any uncontrolled movements of the anus or micturation apparatus which befits the last stage before the sanitation engineers take over after not so much of a wiggle as a nip and a flick of the wrist--as this process begins, as I said, and you're are biting into to these fat rings, try onions without fat, lubrication ducts in the mouth flood forth a salivating juice which combined with the fat pressed out produces a wave of pleasure which needs an explanation.
It is that during our earlier states of being fat was not easy to come by and was an extremely valuable food being high in energy. Hence our evolutionary conditioning to absolutely love it. And here we are with as big a supply of fat available to us as we can eat. And an industry eager to supply any level of demand and not unwilling to stimulate it.
Hence the pornography of the other end. Or, the biology class of a quality atheist school-marm.