Explain to me how this works *spoilers?*

[tyranius]

So basically I was messing with the level editor and was looking at the Daniel's Room map. It's the one where you get the key behind a frame, you have to smash a little glass bottle to get this key.

Well, there's a trigger in this map to spawn a monster after you read a note (or after you pick up the key, can't remember which). Anyways, what I want to know is, how do I know what triggers the monster to appear? I mean, clicking on the monster gives me no clue as to what triggers it.

Thanks in advance!