Yep, it's another "I don't know what I missed" thread...

So I'm doing the Obel Lake sidequest and am following a guide for it as I've never actually done this one before. Having picked up three of the four random letter stones, I can't get the monkey in the forest to throw the fourth one at me. I've done everything this guide I'm following says (spoken to the shadow to get him to mention the monkey having the fourth rock) so is it possible there's something else I've missed?