A frog in his throat

          Why is it that in The Metamorphosis when Gregor first gets up and his mother yells at him, he is able to reply in a relatively normal-sounding voice, but later on when he tries to speak no one can understand a word he's saying?
          A thought I had was that maybe has something to do with everyone's growing concern for Gregor and not necessarily the physical state of his vocal chords. The first time that Gregor speaks after he's been transformed, no one is aware that anything at all is amiss. Gregor is somewhat late in getting up but it hasn't quite yet turned into a huge crisis. He reassures his mother that he's getting up in a mostly human-sounding although slightly gravelly voice that is completely understandable. The next time he tries to speak, no one has actually seen his new body yet, but the manager has come to the house and everyone is suspecting that something must be seriously wrong with Gregor, either physically or mentally, that he would be so adamant about staying in his room. Maybe the change in mood somehow prohibited them from understanding Gregor's speech. At first nothing is really the matter, they don't expect there to be any serious problems, so they have no trouble understanding Gregor. But once they realize something's seriously the matter and once they expect something to be the matter, then they panic and are unable to comprehend Gregor's speech.
          Another possible theory is that the fault isn't in Gregor's audience, but rather in Gregor himself. When he first speaks, he makes it clear that he was trying to speak slowly and enunciate every syllable so that he could be understood clearly. He isn't totally panicking at that point, he's maybe just somewhat surprised about his transformation and worried about getting to work. All he's trying to communicate at that point is reassuring his mother that he's getting up. But the next time he speaks he's very flustered and anxious about losing his job. His boss has threatened that he hasn't been a good employee of late, and Gregor is hastily trying to defend himself. He isn't careful in enunciating his words and he isn't speaking as calmly or slowly as he was before. Maybe no one could understand him because he'd stopped being careful about his speech. Just a thought that is somewhat irrelevant, but interesting; this possibly is an example of Gregor losing his humanity. He quickly loses his resolve to carefully make his speech understandable to those around him.