Sansa asks Littlefinger how and why he had Joffrey killed, and he answers "nothing like a thoughtful gift to make a new friendship grow strong". This is a reference to House Tyrell's words "Growing Strong", who were Littlefinger's co-conspirators.
The scene where Craster's baby son is transformed by the White Walker leader does not appear in the novels, which reveal almost no information about the culture of the White Walkers ("Others") due to their limited interaction with POV characters. However, Craster's wives suspect that their sacrificed infant sons are turned into Others, and refer to them as "Craster's sons".
In the novels, Olenna never admits to anyone that she poisoned Joffrey; Littlefinger reveals it to Sansa after she notices that one of the gems from her hairnet (necklace on the show) is missing, but the books don't reveal whether Margaery is ever made aware of the plot. In The Lion and the Rose (2014), Olenna could be seen fiddling with Sansa's necklace while expressing her horror about how Sansa's brother was killed during a wedding, and one of the poisonous stones on the right was suspiciously missing from subsequent shots. Later, when the wedding cake was brought in, Joffrey gave his cup to Margaery, who placed it on their table, next to Olenna's; it can be assumed that Olenna put the stone into the cup while Joffrey distracted the audience when cutting the cake or humiliating Tyrion again.
The only appearance of Tommen's pet cat 'Ser Pounce' in the series, who was one of three black kittens gifted to him by Margaery in the books (where the conversation between her and Tommen doesn't take place). The cat was meant to show that Tommen is a much sweeter boy than Joffrey, but according to writer Bryan Cogman, it was a "sumo wrestler cat" and "a nightmare to work with"; it was afraid of all the candles and repeatedly refused to jump on the bed. Cogman said that Natalie Dormer nearly wanted to kill him for including the cat, which is the reason why it never appeared again. David Benioff later jokingly stated in an interview with Entertainment Weekly that "Cersei hated the name 'Ser Pounce' so much she could not allow him to survive. So she came up with her most diabolical [execution]. Ser Pounce's death was so horrible we couldn't even put it on the air."
In between seasons 3 and 4, Black Friday (2013) was released, which repeatedly made fun of Game of Thrones' many scenes where characters secretly discuss political intrigue during a walk through the palace gardens. In response, showrunners David Benioff and D.B. Weiss purposely wrote much fewer of such scenes, and even put in a joke where Olenna states that "if I have to take one more leisurely stroll through these gardens, I'll fling myself from the cliffs."