And the curious two year-old did what any sensible toddler would do – he ran like hell to get away from it!
The hilarious footage of the moment has been seen by more than half a million viewers on You Tube.
Little Zack stands stunned as he spies the animatronic dinosaur at a theme park in Texas, USA.
The clever lad informs his mum that the creature stood just 50ft away is a T-Rex.
But when the giant robot roars at them, Zack turns on his heels and disappears into the distance shouting: "Run, run."