his hypothetical ideas on dreams. He described the dream as a fragile equilibrium that is destabilized by the repressed unconscious impulses of the unconscious system, which does not obey the wishes of the ego. Certain preconscious daytime thoughts can be resistant and these can retain a part of their cathexis as well. Unconscious impulses and day residues can come together and result in a conflict. Freud then wondered about the outcome of this wishful impulse: an unconscious instinctual demand that becomes a dream wish in the preconscious. Freud stated that this unconscious impulse could be expressed as mobility during sleep. This would be what is observed in somnambulism, though what actually makes it possible remains unknown. As of 2002, sleepwalking has not been detected in non-human primates. It is unclear whether it simply has not been observed yet, or whether sleepwalking is a uniquely human phenomenon. Society and culture Opera Vincenzo Bellini's 1831 Italian opera semiseria, La sonnambula, the plot of which is centered on the question of the innocence of the betrothed and soon-to-be married Amina, who, upon having been discovered in the bedchamber of a stranger, and despite the assurances of that stranger that Amina was entirely innocent, has been rejected by her enraged fiancé, Elvino — who, then, decides to marry another. In fact, when stressed, Amina was susceptible to somnambulism; and had come to be in the stranger's bedchamber by sleep-walking along a high parapet (in full view of the opera's audience). Elvino, who later observes the (exhausted by all the fuss) Amina, sleep-walking across a very high, very unstable, and very rickety bridge at the local mill, realizes his mistake, abandons his plans of marriage to the other woman, and re-unites with Amina. Jenny Lind and James Braid In August 1847, the famous soprano Jenny Lind visited Manchester, and gave two performances as Amina. The outstanding difference between Lind and her contemporaries was that, "whilst the beauty of her voice was far greater than any other in living memory (thus, the Swedish Nightingale), what really set her apart was her outstanding ability to act"; and, moreover, in performing as Amina, rather than walking along a wide and well-protected walkway (as the others did), she routinely acrobatically balanced her way along narrow planks. While she was in Manchester—on the basis that, at the time, many characterized "hypnotism" as "artificial somnambulism", and that, from a rather different