Back then, Lin Mu had been only at the First Tribulation Stage of the Immortal Realm, thus he hadn't done much during the battle other than trying his best to hide. Of course, even if he wished to he wouldn't do that as that would involve revealing himself when there was no reason to.
Niu Juo had questioned him about this too.
Due to that, Lin Mu had never gotten a proper look at the dagger that Cao Tianyi had used and neither had he had the chance to scan it with his immortal sense.
This was why he didn't recognize it at a first glance.
After all, this wouldn't be the only dagger that was black like this.
"How did you remember this?" Crown Prince Feng Shun couldn't help but ask, as it was simply such an obscure bit of information to keep track off.
