How did O-Chul know?

[elros]

When O-Chul was Redcloak's prisoner and broke free, he knew that Redcloak's holy symbol was also Xykon's phylactery (http://www.giantitp.com/comics/oots0655.html). How did he know that? I don't know of a scene where that information was disclosed in front of him, unless it was in the book "No cure for the paladin blues." Am I missing something, or it is just a plot hole (http://tvtropes.org/pmwiki/pmwiki.php/Main/PlotHole)?

[hamishspence]

He overheard Soon:

http://www.giantitp.com/comics/oots0462.html

[PopeLinus1]

He figured it out one saving throw at a time.

[Chronos]

He's also been talking a lot with Monster-San, who has probably heard Xykon and Redcloak talking about it.