I think walt would have paused after he saw the words "this is michael". It prolly came as a bit of a shock to him and he was taken back for a moment, the same way michael was taken back when he saw the word "Dad?"

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\"We\'re not alone on this Island and we all KNOW IT\" - John Locke

Locke: Why do you find it so hard to believe?
Jack: Why do you find it so easy?
Locke: It\'s never been easy.