Polly washdish, Willy wagtail.

The pied wagtail has several nicknames, and poet John Clare wrote:
'Little Trotty wagtail, he went in the rain,
And tittering tottering sideways, 
he near got straight again.'

They're easy to identify, 
though their constant motion
on a dull day, 
are a blipper's frustration.

You can see at a glance, 
I can do assonance.

Have a good weekend, y'all.