Calamus-induced overlay experience?

[no_leaf_clover]

I came across a mentioning of a plant called Calamus or Sweetflag that's very common and is supposed to produce some subtle psychoactive effects when eaten, and when I went to look up more about it I came across this experience:

Drove up into the mountains with some friends, some calamus root, a flute, a loaf of bread, and some smoke. We ate the root, smoked the smoke, ate the bread, and the laid about with flute music filling the forest. It was a wonderful evening. No weird effect from the root it seemed. Just watching nature. Then we were leaving in the car along a scenic route past about three waterfalls. At about the second one the car comes to halt and the driver yells 'LOOK!'. The water fall had transformed itself. The rock under the falls was a giant easter island like statue who was drinking up all of the water. It was staring at us. At the same time I could see the normal waterful, it was like looking at two worlds at the same time. Both existed, I could function and act normal, but there was this other reality superimposed over the one I was in. I could see into it, and the being there could see me and knew that I could see it. We oooed and aaah for some time and then went home in a somber mood.

http://www.erowid.org/experiences/exp.php?ID=2461

As soon as I read that, the first thing that came to mind was Frank's mentioning of overlay phasing experiences.

What's strange about this plant in particular is that it apparently doesn't produce very noticeable effects. Submitted experiences seem to be more along the lines of catching fairies out of the corner of your eye, or seeing little gnomes scattering across the road as you drive or large creatures strolling across mountains, but that's it. Very surreal, imaginative-sounding stuff, and yet no real reports of anything 'intense', as they say. Any of you have any idea as to what exactly might be going on here?