>>Another one, which is actually two. What's the plural of 'mouse' and 'louse'? 'Mice' and 'lice', right? Two don't make a rule yet, but... let's try:
>>
>>mouse - mice
>>louse - lice
>>spouse - spice
>>nouse - nice
>>douse - dice
>>house - hice
>>twouse - twice
>>polouse - police (OK, this is a bit stretched)
>>rouse - rice
>>ouse - ice
>
>You left out Foot/Feet and Tooth/Teeth. Can't think of any others.

That's a different type, which would deserve a rule for itself: boot-beet, root-reet, soot-seet, booth-beeth... enough to set a rule.

Also, from ox-oxen we could derive box-boxen and fox-foxen :)