Possible Clues:

• Short poem involved magpie eating snippet of roll
• Witty words
• Mrs Simpson turns up, inspiring good piece of wit
• Butt of joke, beastly pair's quip
• English farm animals bring about witty remark
• Saying one animal rears up to protect another?
• Quippy remark
• Witticism spread round to entertain Greek character
• Pointed remark about age - prim rejoinder
• Concise, witty remark