What the visitor said

An island holds two hundred people. Each of them has blue eyes or brown eyes. Each can see everyone else's eyes and never their own, and there is nothing on the island that reflects. No one may say a word about eye colour — not a hint, not a glance, ever. They are perfect logicians, and each knows the others are too.

There is one law. Anyone who works out the colour of their own eyes must leave on the ferry that calls at noon the next day.

The ferry has called every day for as long as anyone can remember. Nobody has ever boarded it.

One hundred of them have blue eyes.

On a Tuesday a visitor comes ashore, addresses the islanders all together, and — meaning nothing at all by it, simply making conversation — says:

> I can see someone here with blue eyes.

She has told them nothing. Every islander on that beach could already see at least ninety-nine blue-eyed people. Not one fact about the island changed when she opened her mouth.

Something happens anyway. Say exactly what happens, say exactly when, and prove it.

Cryptic problems are posted here as they were found. Deciding what the question actually is counts as part of the problem.

Open. No solution has been posted yet.