Final answer:
George encounters a lifelike simulated lion within a virtual reality nursery, which scares him and his wife, Lydia.
Step-by-step explanation:
The wild animal that George encounters and which frightens him greatly is a lifelike lion, found within the virtual reality nursery in his home. This high-tech nursery can create any environment, including the African veldt, complete with realistic lions. George's friends likely did not believe the danger because the lions are just realistic simulations, part of the room's immersive experiences designed to entertain and sometimes test the courage of the inhabitants. At one point Lydia, George's wife, gets so scared by the scenario that she runs out of the nursery, adding to the intensity of their experience within the advanced technological setup that blurs the line between reality and fiction.
The lions in the nursery felt so real that George and Lydia were genuinely scared and ran away from them. This story is from the science fiction short story 'The Veldt' by Ray Bradbury.