I pumped before and all was fine. Then, like always, I hand expressed a little more (I don't know why I do it, but I guess it's just a habit that started when I'd have low supply days). I noticed that milk that was coming out from one of the "pores" on the nipple was oily. Oily as in clear/yellow oil bubbles that stayed separate from the milk. Like oil mixed with milk. It's so weird! I've had that before after a clogged duct resolved itself, but there's been nothing going on there in a while. No pain or anything so I'm sure it's not mastitis, which is what Google suggests.