In Chapter 7, what is ironic about Tom saying that he has second sight?

Even as Tom says “I have a—almost a second sight, sometimes that tells me what to do. Maybe you don’t believe that, but science---,” Nick, and we with him, smile at (or ridicule) Tom’s ridiculous posturing. Even the long dash in the text has meaning, for it indicates the man is unable to see sufficiently into the future to finish his sentence. The dash represents that absence in knowledge that corresponds to Daisy asking what they will do with themselves for the rest of that day, the next, and the next thirty years (125). As if to emphasize this, when Tom pauses (with the dash), Nick says “the immediate contingency overtook him.” “Contingency” means “possibility,” indicating Tom’s limitations are such that the slightest chance in events will leave him speechless, unable to complete a thought.