Beyonce notices Fan's vocal technique, makes them sing!!
This is clip is about 2 years old, but basically it shows how knowledgeable Beyonce is about vocals..She picks a female fan out in the crowd and passes the mike to her saying "yeah you can sing..I can tell by your mouth" She couldn't hear the girl singing a few feet from her, but the way she formed her vowels tipped Bey off that the fan was in fact a skilled singer..When The girl got the mike she belted the house down! Beyonce was impressed..kinda cute
Cute..This is a completely different case entirely, unfortunately..As you could probably hear (or not), Beyonce being the performer that she is, was clearly running out of breath on that legato line (it was 12 seconds long and she had to control the note at a very soft dynamic marking).. so she let the fan finish the note (who indeed sounded horrible)..also this girl actually grabbed Beyonce by the arm and started mouthing words to her..causing her to pause, hence her 15 seconds of fame..she was at the wrong place at the wrong time; this happens many times on tour.
In cases like these, Beyonce can see or hear the person singing below her, from her earpieces and soundbox..she usually hits it with an "excited" facial expression..
Here's more examples..
Beyonce while walking across the stage, heard jamaii from 3 feet away; she heard him harmonizing perfectly under the main melody and purposely walked straight to him intent to hear him sing more!!
I thnik Bey is safe tbh 
), Beyonce being the performer that she is, was clearly running out of breath on that legato line (it was 12 seconds long and she had to control the note at a very soft dynamic marking).. so she let the fan finish the note (who indeed sounded horrible)..also this girl actually grabbed Beyonce by the arm and started mouthing words to her..causing her to pause, hence her 15 seconds of fame..she was at the wrong place at the wrong time; this happens many times on tour.