The words kneading, needing sound the same but have different meanings and spellings. Why do kneading, needing sound the same even though they are completely different words?
The answer is simple: kneading, needing are homophones of the English language.
Present participle of knead.
Present participle of need.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.