Hopefully you will be able to shed some light on the attached photograph.
Having read through the various bird books that I have and searched on the internet I have not been able to glean any information regarding the unusual 'hinging' of the tongue of the waxwing.
From what I can determine from information I have read on this bird, the tongue is triangular, sagittate and papillate at the base. This causes it to flex at the narrow point where the triangular part joins the rest of the tongue causing the hinge effect you mention. It may possibly be an adaptation to allow it to "grip" berries more effectively, however that is just a guess on my part.
Stunning picture by the way
Many thanks for the response. Any idea where on the internet I can read more about this.
If you liked that photo have a look at my website as www.colourflow-images.co.uk