There are really only 133 sounds they can make. That sounds like a lot, but think of all the sounds we make in English. There are 10 right away from 'long' and 'short' vowels, plus 21 (26 letters in the alphabet minus the 5 vowels we already ruled out) consonant sounds, which brings us to 31. 'Sh', 'th', 'ch', which brings us to 34. 'Ar, 'br, 'cr', 'dr', 'er', 'fr', 'gr', ('hr', 'jr', 'lr', 'mr', and 'nr' aren't really ever used in English, so we're skipping it, and 'ir' sounds like 'er', just like 'kr' sounds like 'cr') 'or', 'pr', ('qr' isn't used, and 'rr' is the same as 'r' by itself) 'sr', 'tr', 'ur', and 'vr' ('wr' is only used in 'write' and is in that case the same as 'r' by itself, and 'xr', 'yr' and 'zr' are just plain silly). That gives us 13 more, just by adding the same letter