Just one quick nanosecond glance at her, just one moment of discomfort, and the grand jury will see it.
The grand jury is incapable of seeing any discomfort a person may display. 
mnli hypothesis: The grand jury is incapable of seeing any discomfort a person may display.  premise: Just one quick nanosecond glance at her, just one moment of discomfort, and the grand jury will see it.