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/
Would cats care about red dots that aren't moving? My impression is cats just have a hunting instinct that is triggered by everything moving that is small enough to be prey, including red dots, but only if they are moving...