[ Ah. Perhaps he should have tried to cloak his lie better after all. Or, was it simply too obvious that he's actually quite fond of cats? ]

...you are correct. The third one was the lie.

[ He is completely oblivious to the fact that Hong Lu can tell when he is lying based on his heart rate. But even without that extra information, Hong Lu would surely be able to discern the lie from the rest of his body language.

Even if Yi Sang's words are untrue, his subconscious movements betray him. ]

I do like cats. ...they are gentle animals, but firm in what they like or dislike.

[ And still, his wrist remains in Hong Lu's grasp. ]

Has this illuminated the rules of the game to you?