"It has to be one of these plants we ate in the soup." Jassin said. He was the elf that got ill during the night when they were camping inside the forest.
They did not face any poisonous enemy, so the reason for him getting ill like that was from a poisonous plant they used as a spice, or one person there had poisoned him.
Arthur believed more in the second option, therefor he kept close watch of all the squad members. An elf, a race that lived off the land, and presumably knew all the herbs around their forest, ate something and fell ill? It did not seem convincing.
The four people with Arthur were Jassin, a slim elf, the one that fell ill, Folen, a guy that barely talk with the rest of them, Siora, a gorgeous woman that tried her best to pull out a conversation with Arthur, and the last one, Laeroth, who was the most suspicious of them all, at least for Arthur.