The scene where Sally staggers into a section of the boat filled with dozens (maybe even hundreds) of dead versions of herself.
A chilling moment during the ending. Jess finally broke the loop and is driving away with her son and it seems that all is going to be well, even though something is a little... off. Then, suddenly, a seagull flies into the windscreen, dying instantly. A shaken Jess leaves the car and goes to dispose of the body on the beach... Cue the pile of seagull corpses, as Jess realises this isn't the first time she's done this.
It takes roughly 4 "basic" loops (the yacht reappearing) for every single iteration of Jess to turn into a desperate killer willing to murder everyone who isn't herself in an attempt to prevent the boarding by the people from the 5th loop. To put that into some perspective, a single loop lasts for roughly 20 minutes.
Tommy: witnessing Jess killing her past self. His mom was just brutally murdered... by his mom.
