"Cottleston" is a made up word from a poem by A. A. Milne. A great explanation can be found in the extremely recommendable book
"The Tao of Pooh" by Benjamin Hoff.
Cottleston, Cottleston, Cottleston Pie,
A fly can’t bird, but a bird can fly.
Ask me a riddle and I reply:
“Cottleston, Cottleston, Cottleston Pie.”
Cottleston, Cottleston, Cottleston Pie,
A fish can’t whistle and neither can I.
Ask me a riddle and I reply:
“Cottleston, Cottleston, Cottleston Pie.”
Cottleston, Cottleston, Cottleston Pie,
Why does a chicken, I don’t know why.
Ask me a riddle and I reply:
“Cottleston, Cottleston, Cottleston Pie.”