Gotta be something other than a deficiency. Some sort of bug or the kitty bit that leaf. A deficiency affects all the leaves in the same class not just one random leaf.
Everything else looks great but you should pluck those old dead leaves at the bottom. Possible source of infection or fungus.
EDIT: Just checked out the upper pics more and see it's on a lot of them. Very odd thing going on there. I don't recall ever seeing that and I thought I'd seen it all with pot problems by now. Not sure what to say about it.