Odd word choices that disrupt the flow or feel of a sentence.
Example 1: in a murder mystery novel, the detective is examining the crime scene and is thinking about how the perp "traipsed" into the house. Once was bad, but the author used "traipse" twice more in the same chapter and it didn't fit any of the situations. For one thing, given the conditions of the crime, stealth had to have been involved -traipse does not connote stealth. For another, the detective was supposing that the perp was almost certainly a large male, and I just can't picture one traipsing along to bludgeon a victim.
Example 2: a science news article rather than a book, but the reporter used "monkey" to mean "interfere (with)" and then in the next paragraph used "monkey" when referring to a study involving primates. That word really stands out and there are plenty of better synonyms for interfere, particularly if monkey was going to be used as a noun later.