Stupidity: The fact that Mr. Furley just gives Wally (a total stranger) a presumingly long ride out of town to a farm to see Jack is a bit unbelievable considering the odds are that the trio would not have given (or be obligated to give) Furley the address where they were staying (Larry just shows up too separately). Also, Wally leaves the barn alone at the end... how is he going to get back that same long distance? Although entertaining, lots of stupidities were in this one episode.
Stupidity: The fact that the young mother in the hospital would give Janet (a total stranger to her) her baby to watch while visiting her husband in a different area is completely unreal. Nobody would really ever just give their baby to a stranger like that and leave. In addition, Janet took the baby into Jack's room for quite awhile.
Answer: I believe you are referring to the artwork of Alphonse Mucha. On the wall next to the front door was "Feather" (which is one half of "Primrose and Feather"). Above the telephone in early episodes was "Zodiac". Also seen through The Apartment was "Spring" and "Autumn".