During a discussion between Magdalena and Joona, 'Moomintroll' is mentioned. Moomintroll is the central character in a series of books by 'Tove Jansson'. There have been several television programs based on the character and the books.
The trivia item below may give away important plot points.
There are some rather telling parallels to the 1985 White House Farm murders in Essex, mainly: the presence of an adopted brother and sister, both with psychological issues; the relevance of feet being clean or not.