I quite like this question. It make me wonder rather a lot. And dither.
In fact I dithered almost hopelessly on on this one. Should I pick a UNIQUE index because that's the only one I can't find a reason for, and some of the earlier humour questions have made me think I'll never understand American humour? Then I was wondering whether an XM[as]LIndex might be the one (is there anything humorous to an American in substituting "LIndex" for "as" - is LIndex perhaps some American brandname the rest of the world has never heard of, like whatever it is we are calling those short articles that fill the gaps, that might be humprous in a Christmas context? Or could it even be a spatial index - but no, to get round all those chimneys in the available time Santa would need a hyperspatial index - or could the omission of "hyper" be an example of US humour?
But then I picked filtered, becuase it's the only one for which there's a good sound non-humorous reason! Oh dear, apparently American humour, as before, is something that this poor Scot can't see the humopur in! But I can't complain, I got my seven points.