“There’s no art
To find the mind’s construction in the face:
He was a gentleman on whom I built
An absolute trust.”
(Macbeth by William Shakespeare)
This is one of the best examples of dramatic irony. In this case, Duncun says that he trusts Macbeth not knowing about the prophecy of witches that Macbeth is going to be the king and that he would kill him. Audience, on the other hand knows about the prophecy. This is how it demonstrates dramatic irony.