The E3 showfloor has tons to see and do, from game demos to giant character statues. Certain games have special performers and cosplayers to liven up their booths, and some, like Horizon: Zero Dawn, go all out.
Patrolling the Sony corner of the showfloor was a massive Watcher from the game (one of the robot dinosaurs Aloy defeats in the E3 video). It looked anything but human, although there was a person inside, as it romped around spurting out mechanical creeks and screeches.
The Watcher, as it does in-game, scans for threats with a large, glowing eye that turns red at the sight of danger. At E3, the Watcher would alert its handlers to people wearing Xbox shirts or Nintendo Vans, shoving its eye above them and bathing them in red light. Once assured there was no trouble, its handlers would tell the Watcher to stand down. It lowered its head meekly and returned to its patrol. Another time, a Microsoft employee walked in its path and it instantly went into alert mode.
Just an example of some of the cute, playful competition happening around the showfloor.