Saw it.
Feng Yu clearly saw the invisible knife.
When Cheng Liao rescued him from the troubled middle-aged man, he left a knife wound on the man, but the knife did not exist: Cheng Liao did not have any knives on his body, and no hidden tools were found at the scene.
Feng Yu just saw him put his palm against the man's body, and the man was stabbed.
There may be a knife in Cheng Liao's body, and he can pull it out anytime and anywhere if he wants.
Like some kind of myth, some kind of metaphor, some kind of great fallacy left by the Creator in this modern scientific world.
Concept: All relationships can be cut off. What you think is profound may not be that profound one day when you escape from that situation.