Title text:
After a lot of analysis, I've determined that they're actually big red dots; they're just very far away.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3212/
Probably rfp. Maybe localized to mitochondria or something? Which protein are you tagging? What cell line are you using? Where's the scale?