Chapter 1 of In the Time of the Butterflies is filled with foreshadowing. One example is when the interviewer stands before the portraits of Minerva, Patria, and Maria Teresa. Although she does not mean it the way Dede interprets it, the interviewer asks her, "And where are you?" This quote foreshadows that all the sisters will die except Dede, and that Ded will often torment herself that she had not been with them when they are killed.
Later in the Chapter, the whole family is sitting in the front yard, telling stories. Papa plays around with the girls about how the three oldest, Patria, Minerva, and Dede, were born in such close proximity, one after another, saying "Bang-bang-bang...aiming a finger pistol at each one, as if he were shooting them, not boasting about having sired them". Although it is Maria Teresa and not Dede who is martyred along with the other two, his action foreshadows that three of his daughters will be killed.
In that same conversation, Papa says about Dede, "She'll bury us all". Indeed, Dede does outlive her parents and all her sisters, being the only one alive in 1999 when the story in the book is retold.
I am not sure what you mean by "strange" details, but some unusual and especially effective details in the chapter include the image of "a kitten (lying) recklessly under the runners" of the rocking chair, repeated references to the anacahuita tree in the Mirabals' front yard (the family sits "under the anacahuita tree", and Dede tells the interviewer, "where you see a great big anacahuita tree, you turn left"), and vivid descriptions of the many different, exotic flowers Dede handles as she is waiting for and talking to the interviewer, including "her bird of paradise (on) its dead brances" and "a silk orchid in a vase on the little table below them" (Chapter 1).