The spirits of the two trees you destroyed with your jackhammer live on in the collar you made out of them.
The collar keeps whispering, "Eric (えり)!" into your ear. Your name isn't Eric (I mean it could be, in that case wow, weird, right?), so you assume one of the trees you killed was named Eric. But that's the only name you hear, so maybe they were both named Eric? It's weird.