spoiler warning, plus... some scenes may be discussed out of sequence. i'll try to get as close as possible to the way the movie progresses.
back at paul's hotel (the one he owns), rosa's mother has arrived. rosa's parents used to run the hotel. in fact, rosa's mother is quite disappointed in the way the hotel looks these days although it is definitely nicer than the building across the street where paul has the apartment.
rosa's mother is portrayed by maria michi. she bustles in with her suitcase, and her plans for rosa's funeral.
she has planned funerals before. although she certainly is very sad to lose her daughter, she's determined rosa's funeral will be more respectable than her death.
as for rosa's father, he is very sick with asthma. his doctor refused to allow him to travel. this is what rosa's mother tells paul when she arrives. paul accepts this without much comment.
rosa's mother spends some time looking through rosa's purses. finally, paul asks her what she's looking for... she replies that her rosa would have let her know, somehow, why she wanted to take her own life. paul tells her she won't find anything like that. rosa's things are neatly arranged on shelves that go all the way up to the ceiling.
as rosa's mother unpacks, she shows paul the things she brought with her. he comments she has everything they need (for the funeral) in that suitcase. this emboldens her to bring up her desire to bring in a priest.
paul absolute refuses because he says rosa didn't believe in it, so it shouldn't be at her funeral. her mother continues to insist that it is important. this causes paul to pick up her suitcase and throw it. he was just humoring her before...
later, paul is on the couch downstairs. rosa's mother comes and sits in a chair beside him. she tries to reach out to him and places her hand on his arm. he orders her to move her hand away.
she then begins to complain about a guest who's practicing his saxophone, hinting broadly that paul should run a tighter ship. paul decides on a unique strategy, he turns off all the lights.
paul laughs how the guests are afraid of the dark, just like children. rosa's mother nervously asks him to turn the lights back on as the guests creep out of their rooms.
paul decides he should introduce rosa's mother around (in the dark). one guest he calls "miss blowjob of 1939". he says that still makes her popular with some people. everyone is given names and many of those names relate to people's drug habits. one person he says was his and rosa's dealer. after a certain amount of mother-in-law freaking out, paul turns the lights back on and she decides to just leave him alone.
the next day, rosa's mother meets a guest she likes: marcel (massimo girotti). marcel was one of rosa's lover.
when paul goes to visit marcel in his rooms, they discuss how much rosa tried to make them alike. she got them the same robes, she made sure they both had jack daniels on hand for her (marcel admits he doesn't even like bourbon).
paul learns that marcel has a job clipping certain things from magazines and sending them in... (paul comments that it's an educational job).
marcel tells paul that one night rosa begin clawing at the wall. he only stopped her because she was breaking off her fingernails.
marcel tells paul his with rosa affair was finished before she died. paul says he knows all about it because rosa told him everything.
in fact, paul and marcel seem to be getting along pretty well. then, marcel demonstrates how he stays fit... he has a portable chin-up bar. this causes paul to doubt whether marcel was worthy of rosa and leave.
along this time, paul finds rosa's cigar box of trinkets ... all things that belonged to men. he thinks they are probably souvenirs from her encounters, but thinking he knew everything... paul realizes rosa not only kept this secret; she hid the evidence.