Frank was unfaithful during their 1st separation
- Frank tells Claire in the 1st book that he would understand if she'd been unfaithful during their time apart. Later in the series, when Claire returns to Frank, it's Frank that's unfaithful - leading to the Unfortunate Implications that Frank may have been unfaithful during their 1st separation.
The Craigh Na Dun stone formation is a Guardian of Forever
- Different shape and less talkative, but nonetheless a (for lack of a better word) individual of the same (ditto) species.