He wanted to get back into the passageway, and he did not want the German to see him doing it.

As he thought, he studied the entrance attentively.

And he was startled suddenly to find that he could not see it! Had something happened?
Had the door closed automatically?
If that were so, he was in a nice fix, and he would soon join Boris as a prisoner.
But then he realized that the seeming disappearance of the opening was simply the result of clever screening, by means of bushes.

It had deceived him for the moment.

He saw that the door was so contrived that anyone emerging from it would seem to anyone even a few feet away, to be simply coming out from behind a bush.