First; what looks like some intense conversation occurred between the two.
And then later "the look."
"We typically don't see such serious and stern behavior from Kate," Susan Constantine, human behavioral expert and author said. "This gesture — smirked eyes and a turned down mouth — was a rather dignified way to reprimand Camilla."
Sources: The Good Housekeeping tweet Good Housekeeping Glamour
ONTD: did you ever give "side-eye" at a public event?