That was the last event of nightfall, it would have been Harpo's vial that was used. It could have conceivably been ordered by JP or JL. If no one steps up as Harpo we have to consider Harpo is now dead and the vials have turned up in the mafia's hands since no one is claiming to have them so far.
This is Cat's first post after night and he is obviously trying to say that he was given the injection. Interestingly it is one of the first and only posts in the game by him that has been written in a clear manner.
That is Cat's next post which is when the new posting style began.
So if we are to believe that Cat was injected by Harpo and as Bob said "
The victim has a completely opposite point of view as to their purpose in life..."
Did the injection have him switch sides?
Did the injection force him to respond to posts by typing the opposite of what he really wanted to say to get his message across?
the eyes begin to see
Please entertain the second because Bob's rules have a little loophole that only infers what Harpo's vials do. Sure they usually do that, but he said what they did were a "wild guess" as to which number does what. they did and that leaves the opening for the possibilty above.