In Thai, however, aspirated and unaspirated p are as different as English l and r. Using one in place of the other completely changes what word you've uttered (for example, from 'forest' to 'split'), just as replacing l with r in English would change lip torip. Because English has different rules for the use of aspirated and unaspirated p, an English speaker learning Thai will make the same sorts of mistakes that a Japanese speaker makes in using English l and r.