There was a time in Irene's career as an apprentice when she was petrified at facing a single goblin on her own. She recalled when she thought she had only just woken up from dying and being nearly paralyzed with fear at goblins in the forest near her home.
Back then, the goblins seemed so peaceful compared to what she was facing now. Even though they had just found travelers in the forest and had torn them apart, it was nothing compared to the organized horror the goblins were bringing to them.
She could tell that there was something different about them. Her only assumption was that it had to do with the poison and smoke. Perhaps the two were one and the same, and the smoke was the product of one.
When she, Felix, and Leif followed the knights and mages into the forest, they never told them what they discovered.