Egyptian Plover or Crocodile Bird 
cleaning Nile Crocodile's teeth

This is a digitally constructed image from the Warren Photographic Image Library of nature.  It illustrates the popular myth attributed to Herodotus, 5th Century BC. Two eminent ornithologists (Richford and Mead, 2003) have supported this story anecdotally, but the behavior has never been authenticated.  There are no actual photos of the behavior, but there have been many illustrations.

We normally see a crocodiles as a vigilant creature that would snap its jaw at any movement around their mouth area. It would be such a engaging sight to see a small friendly bird cleaning the teeth of such a large aggressive creature. To capture this myth in action, the type of person that it would come from would be a very patient person. Waiting and waiting for years even, just to see the truth and if the truth were exposed from this journey, it would be well worth it.