I've already mentioned that the Sunday strips were almost certainly not done on the same schedule as the weekday ones, which is why this Sunday strip mentions that Lucy has been going all week even though she has been seen without the ball in a couple of the intervening weekday installments.
I'm not quite sure why Charlie Brown sees Lucy's quest as a threat to his sanity. Maybe it has to do with the noise, or maybe he sees her possible accomplishment as a threat? Maybe he just doesn't want to live in a world in which a little girl can bounce a ball for an entire week. (Speaking of which, doesn't she sleep?)
I am not sure, but this may be the last strip in which Lucy refers to herself in the third person.
