Some species evolved without certain chemicals in their background, or with them causing no effect. Therefore they never evolved a receptor for it. Meanwhile others had to identify toxins or marker chemicals immediately and are highly sensitive even if it’s unnecessary -ie bitter vegetables -. This leads to nonplussed galactic citizens wondering why the deathworlder took a bite of that boring stuff and immediately gagged or refused it entirely because it smelled like pure evil.
Food unites. Meals shared tend to lessen tensions amongst the participants. Excluding, of course, the occasional tension caused by differing definitions of ‘table manners’.
The Aphemii had put on a feast of their own native foods. They had been extremely careful in selecting the dishes that would cause the least amount of trouble to the most amount of visitors. Everything in the buffet was entirely digestable by every visitor.
Gauz couldn’t help but notice how the humans gave the Helgoq-leaf wraps a wide berth. She could see each and every one of them shy away from the display as if it burned them.
As host, it was her duty to find out what offended. She sidled up to an Ambassador known for her honesty and murmured, “My pardon, Ambassador Shayde… what is the error in our menu? I have witnessed all humans avoiding the Helgoq-leaf…”
Caught in a huddle of fellow plus-one’s, her nigh-perpetual companion Rael urgently made no-no motions at Shayde.
“Th’ green sausage things?” she pointed. “Aye. Yeah. Uh… To be real honest… they smell like satan’s arsehole after a bad curry night.”
Rael smacked his own forehead.
Gauz took that to mean that the scent was highly offensive and resulted in instinctual revulsion. Interesting.
 Manners in the Galactic Scene are so wide and varied that, in a multicultural arena, they have to be ignored. So long as another cogniscent is not getting their nutrient content on anyone or anything else, then you have no real reason to complain.