I was told in my class that "They flee from me" is written in iambic pentameter, except for line number 6 in the second stanza in iambic tetrameter. However, some lines in my textbook have more than 10 syllables.
They flee from me that some-time did me seek (this is fine)
With na-ked foot stalk-ing with-in my cham-ber
That now are wild, and do not once re-mem-ber
I end up in in the previous two lines, and some others, with 11 syllables with the last syllable unstressed.
And this is the line that is supposed to be in tetrameter:
And therwithal, so sweetly did me kiss,
The extracts are taken from The Penguin Book of English Verse anthology. It is worth mentioning that I found the poem modified slightly on some websites.
How to justify this pattern in some lines of the poem? Is this a special kind of foot that I am not aware of? And how did my instructor conclude that the foregoing line is written in iambic tetrameter?