Possible Clues:

• Speaking test
• Enunciation challenge
• It is pronouncedly difficult to say
• ''Are you copper-bottoming 'em my man!'' ''No, I'm aluminiuming 'em, Mum.''
• Test of verbal dexterity
• This can bring about stuttering and woe
• 'I wish to wash my Irish wristwatch', perhaps
• Eg, the sixth sheik's sixth sheep's sick
• Peter Piper picked a peck of pickled pepper, for instance
• It's hard to express just how tricky this is