The spelling of the two words "pie sky" may seem strange, but it can be explained through IPA phonetic transcription. "Pie" is pronounced as /paɪ/, with the diphthong "ai" representing the long "i" sound. However, the "i" in "sky" is pronounced as a short "i" sound, represented as /skɪ/. This difference in vowel sound creates a contrast between the two words, despite their similar spelling. The letters "y" and "e" can both represent the short "i" sound in English, adding to the complexity of English spelling rules.