Maria Walsh in her book Art and Psychoanalysis says:
Uncanny sensations are triggered in the present by the creepy evocation of a past that the subject has repressed, a past that should have been over and done with, but which comes back to haunt the subject, making time and space seem out of joint. The ambivalent nature of the uncanny can be seen in the tripartite linguistic play that Freud delineates in his essay.
Does anyone have any information about Freud's tripartite linguistic play? I did not find anything about it on the web.