Tribble neuterator
A cereal box with a tribble neuterator
A tribble neuterator was a type of tool that was apparently used for neutering tribbles. It consisted of a device operated by a turned key.
According to a commercial for Tribbles cereals, each box contained a free tribble neuterator inside.
This was labeled on the boxes of each flavor, including Original Flavor, Hairy Berry and Spicy Ranch. (ST: "The Trouble with Edward")
This cereal commercial was presented in a post-credit scene of the aforementioned Star Trek: Short Treks episode. The context of the commercial from the in-universe perspective is impossible to determine, and may not have been meant to be taken literally.