This is the first episode of the series not to include any scenes set in Mary's apartment.
This is the only episode of season 3 that Valerie Harper does not appear in.
Lou is in the hospital to remove shrapnel he got during WWII. He couldn't have served in the war as Ed Asner was only 15 when WWII ended. However Lou is 46 in 1972, so he was over 18 before the of the war.