Pooh Moon is a play on words (Blue Moon). However, the characters never refer to a blue moon but frequently refer to a "Honeymoon."
Caws and Effect is a play on the phrase "Cause and Effect."
While the relative size of the characters is pretty inconsistent in the series, we get a good sense of the size of Piglet. When Piglet jumps in the picnic basket full of corn, he appears roughly the size of an ear of corn.