Shows you how many pets of each rarity are in a trade.
Upon adding pets to a trade (or viewing an existing trade), a series of numbers will appear in the top-right corner of the corresponding trade section. Each number represents how many pets of a specific rarity are present in that section. The rarity is indicated by an emoji above the number, and you can hover over it (or long-press it, if you're on mobile) to see the rarity label fully written out - e.g. "OMG so common".
Check out the image below for an example of what the rarity counts look like for this very large trade - and feel free to double-check them yourself! 😜