"Yaffle", one of the many strange colloquial names for the Green Woodpecker, refers to the laughing cry of the Green Woodpecker, one of those woodland bird calls easily recognised when heard.
I was fortunate enough to have a close encounter with this our largest Woodpecker, in fact Two Green Woodpeckers while I walked my dog in our local woodlands, most of my encounters usually occur when I have flushed one while it's been feeding in the grass unseen, resulting in a rear view as it flies away. ( never with a rider )
For a change these were too intent on their own domestic dispute, not noticing me for a few short moments.
I first thought that they were a breeding pair, but on closer inspection they appear to be two males, probably in a border dispute, male Green Woodpeckers have a red centre to there moustatial stripe which can be seen in the photograph.
Quite a spectacular looking bird when seen up close.