Dramatic Irony is a situation in a drama wherein the characters in the play cannot grasp what's happening, but the audience can already understand what is going to happen and understood what has happened. So the answer is, Audience knows something the characters don't know.
Ovid created suspense in "Pyramus and Thisbe" by dragging on Pyramus discovering the fate of his love which was all untrue. He did this by using many sentences that eluded to this discovery, causing Pyramus' death. Suspense is further carried on by Thisbe now having to discover her lover close to death, promising her own downfall in the name of love.
