Interesting! I hadn't thought of it from that angle. (That is, about why he'd want to wipe her memories in the first place.) If it's a Men In Black flashy-thingy sort of deal where it's about weird shit getting out, I guess that makes sense...but my question was, does the Doctor generally do that? I mean to some extent there are UNIT cleanup crews who probably are all "nothing to see here, it was totally swamp gas." But he wiped Donna's mind because he thought it would do *her* damage to keep them, not because he thought she'd tell all. So maybe he's thinking of Bill as a bystander still at that point, and then switches to "she's a friend/she matters"? Then again the offer to take the memories was after she said she was hurting and he'd vetoed the "go fix it with time travel" option.

Huh. Hm. Hmmm.