Fletcher's Avian Nausea Index
This is a handy reference guide, possibly aimed at doctors and other medical practitioners, including perhaps vets, aiming to quantify degrees of sickness and nausea, in which being sick as a parrot is officially graded at number five on the "wishing yourself dead" scale. Number One is held by the Great Combovered Eagle, a bird capable of vomiting over three countries simultaneously.
Doctor Mossy Lawn is certainly familiar with this text, diagnosing the Librarian's encounter with a poisoned banana as rating number five - sick as a parrot.
Annotation
Which, coincidentally, is a common cliché in the post-match interview with verbally concussed professional footballers. Reference to the opposite condition, the elational state of "being over the moon" in Unseen Academicals is still being sought.