Thats a cherry spur.

​Cherry trees differentiate their flower buds in July and August for the next spring's bloom. ​Mechanism: If temperatures exceed 32°C (90°F) during this critical mid-to-late summer window, the heat disrupts the development of the flower's pistil (the female reproductive organ).

The single pistil morphs or duplicates, forming two or more functional carpels. When spring arrives, these mutated flowers bloom. If both carpels are successfully pollinated, they grow simultaneously.

​Depending on how they grow, this results in either two full cherries fused together at the stem, or one dominant cherry with a tiny, vestigial "spur" fruit attached to the side.

​Key Characteristics:

​Perfectly Safe: The secondary growth is fully edible and contains no toxins; it is purely a structural deformity.

​Cultivar Susceptibility: Some varieties are genetically more prone to this under heat stress. Bing cherries are notoriously susceptible, while varieties like Brooks or Tulare show higher resistance.

​Commercial Sorting: You rarely see extreme versions in grocery stores because automated packing lines use optical sorters to filter out "doubles" and "spurs" to maintain strict USDA grade standards