Doll in a doll's house
Some critics see Torvald as another doll in the doll's house. They point out that he is as restricted by his chosen role as Nora is by hers; and that he is sheltered by Nora and Dr Rank from disagreeable truths, as a child would be. As Torvald uses Nora for amusement and as a decorative and beautiful object, so Nora uses Torvald as a provider of money and security.
Big black hat
In this light, it is significant that Torvald tells Nora to practice the Tarantella while he shuts himself away in his office: "I shall hear nothing; you can make as much noise as you please." While Torvald is ostensibly being indulgent towards his wife, the image of her practicing this passionate dance alone and unheard emphasizes her isolation within her marriage. She persuades him to watch her practice the dance in order to prevent him opening Krogstad's letter. He tries to rein in her wildness with his instructions, but she ignores his comments and dances ever more wildly, her hair coming loose. The mythology of tarantism suggests that she is dancing in order to rid herself of a deadly poison. Depending on how we wish to interpret this symbolism, the poison may be the threat posed by Krogstad's revelations, or the poison of deception and hypocrisy that characterizes the Helmer marriage.
Light also appears to symbolize hope and spiritual redemption when Dr Rank is talking in code to Nora about his coming death (Act 3). He talks of death as a big black hat that will make him invisible, an image of obliteration of life. But Nora brings him a light for his cigar as she wishes him goodbye. Dr Rank loves her, and in spite of her sometimes dubious behavior towards him, she has given him understanding, compassion and acceptance. She also means at this point, it seems, to join him in death by committing suicide. Their bond is represented on stage by the image of them standing together in the pool of light from her match - a frame that excludes Torvald.
By Christmas Day, the tree is stripped of its ornaments and its candles have burnt out (a link with the symbol of light). By this point, Torvald has refused to keep Krogstad in his job and Nora feels sure that Krogstad will reveal all to him. The carefully maintained appearance of the happy marriage is disintegrating under the encroachment of truth.
New Year's Day
Other characters too enter new phases in their life. Mrs Linde and Krogstad begin their life together after long periods of suffering, and Dr Rank dies, which can be seen as an end or a transition, depending on one's viewpoint.
A Doll's House: Metaphor Analysis