In "The Edible Women" What do Peter's and Marian's different understandings of the heart-shaped cake (chapter 23)?
what it tell us about the respective roles they play in their relationship?
Marian got that cake for Peter knowing deep inside it was more of an obligation as a girlfriend than out of genuine love for him. The cake is totally cliche: Pink, heart shaped, cute, and "probably stale." To Marian, the cake was just like her relationship and engagement to Peter: Obligatory, cliche, nice to look at, but deep inside it is stale, getting old, flat, and tasteless.
To Peter, since he is clueless about everything, the cake is just that: A cake. He ate it, and as he did this, Marian realized for sure that Peter would fail every test and challenge she places upon him: She wondered if he ate the cake whether he'd be as normal or abnormal as her. He failed the test when he ate the cake unknowingly. She realized there and then too that they simply were not in the same page.