You start down the tunnel through the thicket, your feet crunching on branches below. The path is invisible to all but Kahan. To the rest of you it appears but a blur, and as though you are walking through the briar. Therefore, Kahan takes the lead with Borimer close behind. They are followed by Leo, Vuzyl, and Tahldar. Shapfren walks just in front of Shae, who once again takes the rear.
You make it perhaps 50 feet before things start happening. In the darkness of the cavern, it appears that the small, thorny bushes are moving or swaying to block your path, as if by a wind.
But then you notice that they are approaching you with branch appendages filled with thorns. Each of the creatures blends in perfectly with the surrounding black thorny bushes, but when one steps in front of you, you can see it more clearly. It is about 5 feet tall with two branches extending down like legs and two more out like arms.
The briar around you stirs as several more approach. (Pushing out of the tunnel from Kahan will invoke the rules above. There appear to be six approaching, two from each side, one from the front and one from the rear. They approach cautiously. Their reach is about 6 feet with their elongated arm branches. Axes, scythes, etc. get +2 to hit/damage; swords or other blades get +1 damage/to hit; blunt weapons get -1 damage/to hit; projectiles get -2 damage/to hit.)
As the tree monsters attack, the humming in the distance seems to grow slightly louder. You also notice more swaying in the other briar around you, meaning there are definitely more of these things in hiding.