I've always thought it was "then". It sounds nothing like "think" to me. Plus, all of the live recordings suggest it is "then". Some live recordings are actually much clearer than the studio version and they make it obvious that it is in fact "then". Come to think of it (not that they are pieces of hard evidence), not one transcript I've seen deviates from the lyric being "then"....Unless it's "Zen"

Haha. I think from 2007 onwards, he's looked better than he has done since 1996!