Do you notice the thing below the female Red-crested Pochards / Kolbenente (Netta rufina) bill? It’s the tongue of the bird, hanging through the mandible. A condition known as oral or sublingual fistula.
A sublingual fistula is an opening through the ventral skin of the buccal cavity through which the tongue can protrude. The cause is unknown.
Hughes et al. 2013: Sublingual fistula in a masked booby (Sula dactylatra) and possible role of ectoparasites in its etiology.
Sublingual fistula in a female Red-crested Pochard Common | 18.5.2022 – St. Andrä am Zicksee, Austria 
Sublingual fistula in a female Red-crested Pochard Common | 18.5.2022 – St. Andrä am Zicksee, Austria