A Vicker was an old Earth slang term for a modified being fitted with cybernetic devices in the brain that allow for recording just about everything, including telepathic communication. The term was derived from an old acronym, "VCR" (Video Cassette Recorder), an obsolete Earth technology. Vickers appeared to have no thoughts to telepaths who scanned them.
Abbut was one such Vicker. [1]
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