A downvote on an answer leads to a floater suggesting a comment. There's a hypothetical problem with this: if I dv and also comment, the subject now has a pretty good clue who dv-ed it. A sufficiently unhinged personage might then go off in search of anything and everything I've ever posted to return the favor.
I am a very infrequent downvoter, but I went ahead and did both just now, having encountered an answer with a flatly counterfactual statement, and now I'll see what happens.
I imagine that someone has suggested attaching anonymous comments to the anonymous downvotes to avoid this possibility.