I was just clearing out the last of the comment spam - I'd let it stew in the database (unpublished) but thought I'd take a quick peek to see if there were any false positives. I thought I'd found one - a comment marked as spam, but with content portraying sympathy with my plight against these spammers - that they must be stopped.
So, without thinking, I clicked "submit ham" - to tell Akismet that it was a bona fide comment. Then, I checked the URL to see which friendly blogger was commenting.
And got a spam site.
The spammer was trying to get through the filters by reading my recent post and trying to get whitelisted by posting something not spamish at first glance. But, Akismet had stopped him in his tracks - until I clumsily intervened. It's now re-flagged as Spam, and banished to that special inner circle of hell reserved for these roaches.