Aposiopesis

Aposiopesis is a figure of speech, in particular a form of ellipsis, in which the speaker breaks off suddenly in the middle of speaking, giving the impression that he is unwilling or unable to continue. It often portrays being overcome with emotion.

Examples

The traditional example of aposiopesis comes from Virgil's Aeneid 1.135:

Quos ego—

meaning, in context, "Such rebels I—". This closely mirrors a more contemporary example of aposiopesis, namely, "Why I oughta...".

Another common example comes from William Shakespeare's Julius Caesar, 3.2.104-107, in which Antony interrupts his own speech at Caesar's funeral:

O judgment! thou art fled to brutish beasts,

And men have lost their reason. Bear with me,

My heart is in the coffin there with Caesar,

And I must pause till it come back to me.