I counter with the facts that USSS are trained to read and possibility to act immediately facial expression inside a glance/sweep of dozens of people within eyesight.
This is no doubt true; were you a USSS agent? :-)
But with this difference - seeing an expression “live” and being able to watch the person through some time (even 2 or 3 seconds), and then look again, gives a much fuller picture of that person than one split second snapshot.