Sonar works by sending a pulse of sound, and then listening for what comes back. Using sound waves both the location and the size can be determined.
Reading heavy material has this effect too: What you are reading is causing the internal is-it-ok radar to pick up many, many echoes. Your nervous system is flooded with pings.
By sending packets of information into your system, you will discover slumbering pockets of big emotions that need to be aired.