I know what an umlaut is in German, and I can understand that there is a
vowel change in the plural that seems to go with the foot/feet thing
we have in English, but could someone explain in more detail exactly
what is meant by the i umlaut. In German you indicate the sound with
two dots over the vowel in question and the sound can also be written by
sticking in an extra e to create the same sound. I'm not following what
is happening with the i umlaut in Old Norse.