What leads Rebecca (Mandy Moore) to the borderline comatose state we saw her in during the This Is Us Season 3 finale has been one of the slowest-burning mysteries the NBC show has ever done — and the show has featured a lot of mysteries over its relatively short lifespan. However, Tuesday's episode — the last before the winter finale next week — delivered the most informative dose of foreshadowing that we've seen all season.

Rebecca arrived in Philadelphia ahead of Thanksgiving to see Randall's (Sterling K. Brown) new home and to get a tour of his new city. At first her incessant picture taking seemed like normal proud-mom behavior, but it became evident over the course of the episode that Rebecca is starting to lose her memory. She nearly had a meltdown over losing her phone in Randall's office, only for Randall to find out later that it's a new phone because she misplaced her old one. In fact, Rebecca's memory loss is so frequent, Miguel (Jon Huertas) has started to call her lapses "senior moments."

Discover your new favorite show: Watch This Now!

When Randall proposed that Rebecca see a doctor, she immediately lashed out at him for telling her what to do. The volatile exchange — a rare occurrence between Rebecca and her favorite son — did nothing to alleviate Randall's worry that his mother was showing the early signs of dementia. The two didn't make up before Rebecca decided to go to bed, cutting off the argument.

The tense conversation put Randall and Rebecca in a very uncomfortable place heading into Thanksgiving dinner, an event that has historically not gone well for the Pearsons over the course of the show. In Season 1, Thanksgiving is when Randall found out that Rebecca had known who William (Ron Cephas Jones) was and that he was still alive. Season 2 revealed the depths of Kevin's (Justin Hartley) drinking problem, while Season 3 delivered the origins of Jack's (Milo Ventimiglia) Vietnam pendant.

Mandy Moore, <em>This Is Us</em>Mandy Moore, This Is Us

This season's Thanksgiving-themed episode is shaping up to be equally epic, if not more so, considering the guest list: Deja (Lyric Ross) has invited her mom, and Kevin will return with Uncle Nicky (Griffin Dunne) in tow.

"I think it's a very unpredictable episode," Griffin Dunne told TV Guide during a recent NBC midseason press event. "Anyone who watches a lot of television and movies knows that most Thanksgiving gatherings, there's going to be some dysfunction... I think there's an incredible balance of story and theme that's even more complicated than they've done. This one is much more of a high wire act. It doesn't follow a cliche of a normal Thanksgiving dysfunction. It's a lot more than that."

This year's Thanksgiving could also give us the first hint of an explanation as to why Nicky was the one sitting at Rebecca's bedside in the flash-forward sequence. However, Dunne isn't at liberty to give too much away about that.

"I know that having me sitting around her bed in the near-ish future wasn't an arbitrary choice," he said. "A lot of thought goes into this, but what brings me there I have a glimpse of, but I look forward to really finding out."

So do we, sir. So do we.

This Is Us airs Thursdays at 9/8c on NBC.