A moment later a low rumbling began, which quickly grew louder. Then the gray outline of a boulder exploded from the tunnel mouth, rolling fast, straight at us, and I suddenly understood the need for that ramp. I jumped away instinctively when the boulder, having hit the ramp, seemed to lunge upward, coming straight at the hole. A moment later—crash! It hit.
In that moment of impact, I had the image of the boulder filling the hole perfectly, like a stopper in a bottle. I expected it to rebound, of course, but it didn’t, because Grendel, who had not stepped aside but had held his hand out in readiness, at the instant of impact, with fingers spread, grabbed the boulder.
I wondered at this, since I thought even his two-foot hand span wouldn’t be able to grip that smooth surface. But I was n
