How can you place a pencil on the floor so that no one can jump over it?

“Lay it flat on the floor”

Laying it flat on the floor does not prevent someone from jumping over it, as they can easily leap over a flat object.

“Stand it upright”

Standing the pencil upright does not stop someone from jumping over it; they can still jump over the top of the pencil.

“Put it in a box”

While placing it in a box might obscure it, it does not address the riddle's requirement to ensure no one can jump over the pencil itself.