When Togashi doesn't write walls of text, we're left in the blur about what happened.
How could Hisoka notice Tserriednich's nen beast and power ? Is it part of his post-mortem nen somehow ? Something is drawn with the eyes but it doesn't seem to be simple gyo.
why not?
this is the laplace's demon nen beast right? did it have a rule that stated it can't be seen by anyone? iirc Theta saw it when it manifested.
And guardian nen beasts are visible to any nen user besides the princes.
And noticing Tserry is prolly because Hisoka is way higher level nen user. He also has a weird intuition that we have seen. Also, Theta had a similar reaction to invisible tserry earlier too.
There's also the fact that if Hisoka saw the laplace's demon nen beast still standing there after tserry "died", he would know that the user, ie the dude he just killed, is most likely not dead, or revived using post mortem nen.