imperceptible

Instead of something like a text message that can raise the alarm and leaves a visible trace, this one was a much quieter network injection attack, a tactic valued because it’s almost imperceptible except to expert investigators.

A team of scientists was pulsing imperceptible ultrasound waves through his skull into frontal parts of his brain, and tacitly controlling which object he looked at.

The nature of the harm allegedly caused by Goddard was “subtle, imperceptible and pernicious.”

The number of straight men who change their name upon marriage, remains so tiny as to be imperceptible.