‘Imaginary menagerie’, say (6-7)
I believe the answer is:
tongue-twister
(Other definitions for tongue-twister that I've seen before include "Phrase that is difficult to say properly" , ""I wish to wash my Irish wristwatch", perhaps" , ""Red lorry, yellow lorry", for example" , "Sequence of words difficult to say" , "Peter Piper picked a peck of pickled pepper, for instance" .)