https://www.reddit.com/r/woahdude/comments/1vehg6/gopro_on_the_back_of_an_eagle/cersffj

Alright here's how it works:

Basically it only works for bots that have been shadow banned (banned from voting/commenting, but they have no idea they've been banned.) This means the bot can post, upvote and downvote all it wants but it will have no way of telling if it's shadowbanned. In fact, you could be shadowbanned right now and not know it. Until I reply to your comment, then you know you aren't shadow banned. The reason they do this is because if the bot knew it was banned, it would just make a new bot and continue exploiting. This way, the bot will keep doing stupid stuff not knowing it's been banned all along, and no new bot will replace it until it finds out.

This is where the reason for fuzzing comes in. Once the bot downvotes, reddit detects it was a downvote from a shadowbanned bot and tacks on an upvote to balance that banned bot's vote. This way, the total upvote count is totally unaffected by all shadowbanned bot votes, and the shadowbanned bots actually think their vote counted (but it did not.) This is vote fuzzing. It also randomly adds both 1 downvote and 1 upvote at random intervals so that the bot can't tell if its downvote just got upvote cancelled, or if it's just reddit doing its fuzzing. The total end count stays totally accurate, but when you see the background numbers (you aren't really supposed to be able to see the background votes) you can see the fuzzing happening.