In the draft:
Across her brain one half-formed thought may pass:
In the final version:
Her brain allows one half-formed thought to pass:
Pound's annotation to the draft of this line is amusing. He corrects Eliot for a mistake likely to be made by many a lesser writer. In the edited drafts you can see where Pound scratched out the word may, circled it and drew a line from there to his note where he wrote:
make up yr. mind
you Tiresias
if you know
know damn well
or
else you
dont.
Citation: "The Facsimile" pp. 46-47