The spelling of the word "twiddy" can be explained using the International Phonetic Alphabet (IPA). It is pronounced /ˈtwɪdi/, with the symbol /w/ representing the "w" sound and the /ɪ/ symbol representing the short "i" sound. The combination of the /w/ and /ɪ/ sounds creates the "wi" sound in the word. The additional "dd" letters in the spelling help to indicate the double consonant sound at the end of the word. Overall, the spelling of "twiddy" accurately reflects its phonetic pronunciation.