Uhura went back to the recording in the twenty-fourth month, on her own time, for a reason she could not have defended.
There is only one recording of the Guardian of Forever. Twenty-two minutes and nine seconds of it, taken through an open channel on a landing party circuit while six people stood on a plain and were told what had happened to them. Starfleet had classified it, and she had it anyway, because a communications officer who cannot retrieve her own channel logs is not a communications officer.
She had listened to it perhaps forty times as language. That night she listened to it as signal.
It was the first time anybody had.
* *
The voice is not a voice. That was established in the fourth month by three linguists on Starbase 11 who had access to a transcript and not to the audio, and who were therefore wrong about almost everything.
There is no vocal tract in it. There is no breath, no glottal onset, no fundamental frequency in any register a body produces. What arrives at a microphone is a pressure wave that has been assembled rather than spoken, in the way that a thing built out of parts is assembled, and it is assembled correctly, and it is assembled by something that has heard speech, and has understood entirely how it works, and has never once needed to make any.
Uhura separated it, because that is what she does.
She pulled it into components the way she had pulled the Beta Aurigae relay apart, and she found what she expected, which was structure, and carrier, and modulation, and no residue.
And then, at four minutes and nine seconds, under the sentence about being a rock, she found the thing that was not supposed to be there.
*
It is not a sound. She was careful about that afterward, and stayed careful for the rest of her life.
It is a variation in the interval.
The Guardian speaks with mathematically identical spacing. Every pause in twenty-two minutes and nine seconds is the same length to eleven decimal places, which is what you would expect from a thing that is assembling speech rather than producing it, and which is the single most inhuman quality of the entire recording.
Except in four places.
Four times, across twenty-two minutes, the interval before a sentence is longer than the interval that follows it. Not much. Between eleven and nineteen milliseconds. Well under the threshold at which a human ear can register anything at all.
Every one of the four falls immediately before a sentence in which the Guardian says no.
*
She took it to Spock at the end of the middle watch, and he examined it for two hours and forty minutes without saying anything.
"You are proposing that it hesitated."
"I am not proposing anything. I am telling you what is in the recording."
"Lieutenant, a variation of nineteen milliseconds in a signal of this kind is within the noise floor of the equipment that recorded it."
"No, sir. It isn't. I know what my equipment does."
And Spock, who had spent two years being right about everything, and had come to understand what that was worth, sat with it, and did not dismiss it and did not accept it.
"Then there are two available readings," he said. "The first is that a mechanism which has stood for five billion years has an artifact in its output which nobody has previously had the equipment or the reason to look for."
"And the second."
"That it did not want to say it."
Neither of them said anything for a while.
"There is no third reading," said Spock, "and there is no instrument anywhere that will separate the first from the second, and there never will be, and I am going to have to ask you not to tell the doctor."
"Why not?"
"Because he would believe the second one," said Spock, "and it would not survive being believed."
* *
It is not in her archive. She checked the rule and the rule was clear: the archive is for what he said.
She wrote it on a piece of note stock instead, and put it in the back of the case with the wooden bird, and it said:
4:09. 7:51. 14:02. 20:38.
Nineteen, sixteen, eleven, nineteen.
It does not want to.
She never showed it to another living soul and she carried it for fifty-one years and she never once decided what she thought.