'Happy Death Day' contains 2 major clues that answer the biggest question of the horror franchise. Here's how to find them.

Warning: There are spoilers ahead for " Happy Death Day 2U ."
"Happy Death Day 2U" answers the biggest mystery from the 2017 horror thriller: Why is Tree reliving her birthday over and over again?
Director Christopher B. Landon previously told INSIDER there were clues in the first film about the big reveal.
Now that "HDD2U" is out, Landon tells INSIDER the first hint was a continuous blackout that happened in the first movie. The other is hiding in the opening Universal logo to the movie.

The sequel to " Happy Death Day " is finally in theaters and it won't take long for the movie to answer the biggest mystery to the first movie: Why was Tree reliving her birthday over and over again?

It turns out, Tree (Jessica Rothe) wasn't having some cosmic revelation. Rather, her time loop was the result of a quantum machine called SISSY developed in part by her boyfriend's roommate, Ryan (Phi Vu).

If you recently watched the first film from 2017, you're able to go back and find a few clues that hint at SISSY,

"So there's two spots," director and writer Christopher B. Landon told INSIDER. "The first one, it was the power outage. And then the second one was actually a sound in the opening credit sequence of the movie, the Universal logo."

Read more: The 'Happy Death Day 2U' director answers all the questions you have after watching the sequel

You may remember that in the first movie, there's a power outage each day at 9:23 p.m. After watching the sequel, we now know that was caused by SISSY. The second clue Landon mentioned is a bit tougher to find and occurs before the movie even really starts.

"When the logo repeats itself, it makes a very big crazy sound," said Landon of how to find the second clue. "That's the actual device powering off.So people actually hear, it's called SISSY in the movie, Sisyphus Quantum Cooling Reactor. That's the sound it makes when it goes off."

Here's the moment Landon is talking about:

Did you catch either of those?