Vowel /ɪ/ is spelled with <i> except for <ei> in forfeit. Vowel /ʊ/ is either <u> or <oo> except for <o> in wolf and <ou> in patchouli.
Both vowels are short and fairly central in the mouth but differ in lip-rounding. There is a slight potential for confusion, but they do not seem to constitute a specific problem for any one nationality, perhaps because most foreign learners will in any case tend to make vowel 8 into a more of a back-rounded vowel than native speakers do.
The mean density values is 0.3%, though this is distorted since vowel 2 is very common while vowel 8 is rare. The list makes 38 semantic contrasts giving a loading of 56%.
Bill bull bill bull bills bulls billet bullet billets bullets billies bullies Billy bully brick brook bricked brooked bricking brooking bricks brooks city sooty crick crook cricked crooked cricking crooking cricks crooks fill full filly fully fit foot fits foots fitted footed fitting footing fitter footer fitters footers forfeit forefoot giddy goody hick hook hicks hooks hid hood kick cook kicked cooked kicking cooking kicks cooks kid could lick look licked looked licking looking licks looks liquor looker liquors lookers nick nook nicks nooks patchily patchouli pill pull pills pulls pitch putsch pitches putsches pit put pits puts rick rook ricked rooked ricking rooking ricks rooks Ricky rookie sit soot sits soots sitting sooting tic took whippy whoopee Wilf wolf will wool wills wools Willie woolly willies woollies
Credit: John Higgins