Gregor had wanted to give a full answer and explain everything but in the circumstances contented himself with saying- I’m getting up now.
The change in Gregor’s voice probably could not be noticed outside through the wooden door, as his mother was satisfied with this explanation and shuffled away
But this short conversation made the other members of the family aware that Gregor, against their expectations was still at home, and soon his father came knocking at one of the side doors gently but with his fist