(Each is unrelated to the others)
The treaty banned the use of mass drivers against civilian targets, the development of biological weapons, and the hiring of Human mercenaries.
"Looks like we'll be at war with the Humans soon. You've been spying on them. What can you tell us?"
"It's grim. The Humans are the best I've ever seen: weapons, tactics, determination, intelligence and counter-intelligence, physical toughness -- they've got everything."
"Is there any good news?"
"They have a tradition of mercy to enemies who surrender."
"They told you to say that, didn't they? They turned you."
"I did say they were the best at counter-intelligence."
The Human ability to hit enemies with ordinary rocks from further than arms' reach is well documented, but is not an example of the supernatural. If you work through the differential equations, you can see that "throwing" is compatible with physics as we understand it.
"Let me get this straight. The Human nervous system is slightly different from ours, so capsaicin doesn't trick it into feeling like everything is fine and you're at one with they universe."
"That's right. We have other chemicals that can do that, but capsaicin just tricks our nervous system into thinking it's on fire."
"And yet you selectively bred the most potent capsaicin-bearing plants in the galaxy. Why?"
"We did it before we started keeping written records. I can only assume it seemed like a good idea at the time."
Halloween is an ancient Human tradition. Allegedly the Veil Between Worlds grows thin, and evil spirits enter the material plane. Human children dress in frightening costumes to scare them back where they belong and are rewarded with candy. What could be more frightening than a Human child in search of candy is not recorded.
The Elves, the Dwarves, the Orcs -- even the Dragons have their own gods, who watch over and protect them. Not so the Humans. Why not? Perhaps because they do not need one.
"Why did you order the retreat? We were winning! At a high cost, but winning. We could have ruled Earth."
"I ordered the retreat because my spies finally returned with relevant intelligence. We were winning, but it couldn't last."
"That was my sergeant's guess. So what was the Humans' reserve anyway?"
"I don't know. My spies didn't get that far. They just told me what the front line was."
"But... we knew what their front line was. We were already fighting that. And winning."
"We knew what they were capable of. But we assumed they were an elite military division. We didn't know they were just a batch of stubborn, 'moderately' armed farmers."
Many have tried to colonize the desert hell-world of Arkakix with its terrifying sandworms. The Arvinia tried to settle only in the rocky highlands where the sandworms do not go, but the wealth is in the lowlands, so they went backrupt and went home. The Preptorians established a heavily-armed society, but couldn't support all the extra industry to maintain it, so they died when their blasters broke and couldn't be repaired. The Abslvents tried to exterminate the creatures, but they mostly dwell underground, and a planet is too big to carpet-nuke.
The humans studied the horrible creatures: their anatomy, their life cycle, but most intensely their behavior. Then they saddled the beasts and rode them from settlement to settlement in place of a proper transit network.
Every race's nature is reflected by how they fight in the ring: the Kwongas' raw aggression, the Vlecnos' cold precision, and the Humans'...
We all laughed when the Humans showed up. They didn't even have exoskeletons. Just skin.
But the mightiest Kwonga warrior can face a few dozen full fights in the ring before his carapace is too cracked to continue. A Human can bring the experience of hundreds of fights.
Because skin heals.