How does the author create and maintain suspense in "The Veldt"?
Bradbury builds suspense through the use of uncertainty. It makes absolutely no sense that the video images projected on the nursery walls are anything more than realistic film of the African veldt. In a rational universe, the images could not cross from the view screens into the real world the Hadley's occupy.
And yet, step by step, Bradbury creates the creepy feeling that this is exactly would could—and did—happen.
Part of how he does this is by having Mr. Hadley provide a reasonable explanation for the nursery after it has frightened Lydia. This reasonable explanation nevertheless leaves the readers saying "but" . . .
Walls, Lydia, remember; crystal walls, that's all they are. Oh, they look real, I must admit—Africa in your parlor—but it's all dimensional, superreactionary, supersensitive color film and mental tape film behind glass screens.
Bradbury has already undercut Mr. Hadley's reasonable conclusion with the vivid description of the lions and the veldt that he provides, so realistic it helps convince the audience the lions just could just be real:
. . . you could feel the prickling fur on your hand, and your mouth was stuffed with the dusty upholstery smell of their heated pelts . . . and the smell of meat from the panting, dripping mouths.
Bradbury continues to build suspense by dropping hints that lead us to suspect something very bad is going to happen. For example, near the end of the story, David McClean picks up Lydia's bloody scarf from the nursery floor. At this point, it seems the "fiction" of the view screens and the "fact" of the real world can converge.
Finally, we have the odd behavior of the children, who seem much more attached to the nursery than to their parents. This also raises the prickly feeling that something is going to go very wrong.