A closer look at the Cormorant and the blue mouth. Explain?

Ok so, I see inside the mouth is blue too.
So cool. But why can anyone explain this oddity in nature.
#themadcameraguy #sonycamera #nature #audubonsociety #naturevideos #naturelovers #cormorant

[@capturingnaturewithsandip]

Nice capture. Thanks for sharing so wonderful video & big like