Human right-handedness does not originate in vocalisation as such but in selection pressures for structuring complex sequences of digital signals internally, as if in a vacuum. Cautious receivers cannot automatically accept signals in this way. Biological displays are subjected to contextual scrutiny on a signal-by-signal basis – a task requiring coordination of both hemispheres. In order to explain left cerebral dominance in human manual and vocal signalling, we must therefore ask why it became adaptive for receivers to abandon caution, processing zero-cost signals rapidly and on trust.