The tag implication #65566 nipple_masturbation -> masturbation is pending approval.
Reason: What? Your Honor, you would like to see the evidence? Well, let me just check the court record real quick...
Take That!
As you can see, that fox is clearly deriving sexual pleasure from the manual stimulation of their own nipples. Therefore, the activity that they are engaging in can be considered a form of masturbation.