How did the mole know that twinkle on the opposite side was not star?

From the text:

As he gazed, something bright and small seemed to twinkle down in the heart of it, vanished, then twinkled once more like a tiny star. But it could hardly be a star in such an unlikely situation; and it was too glittering and small for a glow-worm. Then, as he looked, it winked at him, and so declared itself to be an eye; and a small face began gradually to grow up round it, like a frame round a picture.
A brown little face, with whiskers.
A grave round face, with the same twinkle in its eye that had first attracted his notice.