Plot question in “The Secret History”

I am on chapter 5 of the The Secret History (around page 245)

Bunny drunkenly stumbles into Richard’s room and reveals that he “knows” what is going on.

Is this regarding Henry’s plot to poison him or his knowledge that he killed the farmer? I am getting mixed answers on Google, but I thought Bunny found out (and has known) about the farmer when they returned home covered in blood.

If it is the former, how did he find out?

by LoftyLions