Goofs

After breakfast, Rose puts a flower in the mouth of a bull statue that is sitting on the table. After the cut the flower is no longer in the bull's mouth, it is in the vase with the rest of the flowers.

Given the book that Shirley is writing, Hangsaman, the film is set in 1949/1950. A couple of times Stanley is seen putting on 12" vinyl albums - a very new format at that time. However, the record deck that he uses is of a design and type not seen until the 1970s.

Early in the film Shirley mentions at a house party that she and Stanley have been married for twenty years, this would set the film in 1960. However, the book that she is writing, Hangsaman, was published in 1951, which sets the film a decade earlier. This is in keeping with the clothes and cars seen in the film.

After the extended scene in the forest with the mushrooms, Shirley is later shown as almost incapable of leaving the house (agoraphobic?) And her husband berates her for not stepping outside the house for months and months.

The death cap mushrooms Shirley points to don't resemble death cap mushrooms at all, which are usually white and flat-capped. It's entirely possible this is another example of Shirley's psychological manipulation.