The ending hints, director Amway "Day of the Groundhog"

[repeated scene in the beginning of every day: Ryan enters the room he shares with Carter]

Ryan Phan: [to Carter] Dude, you hit that fine vagine or what?

[Ryan notices that Tree is still in the room, and heard what he said]

Ryan Phan: [embarrassed] Oh, I'm... I'm sorry.

[Tree leaves]

Carter Davis: [angrily] Nice one, dickhead!

[Tree enters the OR, armed with a gun and a knife. Tombs lies on the bed, seemingly asleep. Tree points the gun at him]

Tree Gelbman: I know you are not asleep. Open your eyes.

[Tombs blinks. Determinedly, recalling how Tombs ruthlessly killed Carter the day before, Tree presses the trigger, but nothing happens. Tombs smiles teasingly. Fearfully, Tree presses the trigger repeatedly, but in vain]

Joseph Tombs: [mockingly] Safety on, little girl.

[Tombs strikes Tree with a pillow, knocking the gun from her hand. The gun slids on the floor out of the room. Tree attempts to retrieve it, but Tombs charges, grabs her and slams her against the wall. He starts strangling Tree, but then he notices the knife in her belt. He draws the knife]

Joseph Tombs: Look what we have here... hmm?

[Tombs presses the knife against Tree's throat. Tree whimpers. Tombs moves his face near Tree's cheek]

Joseph Tombs: You know, it's a real nice surprise, you comin' and visit me like this...

[Tree knees Tombs in his groin. Tombs recoils painfully, then attempts to stab Tree. Tree evades Tombs, and the knife is thrust into the door. Before Tree can get away, Tombs grabs her and slams her against a door in the opposite wall, then throws her against a firehose cabinet. The glass door of the cabinet breaks. Tree collapses on the floor, groaning in pain, among glass shards]

Joseph Tombs: Woof! I like you. Damn shame.

[Tombs pulls the knife out of the door. Tree tries to stand on her feet, but she is too weak]

Joseph Tombs: You're a fiesty little shit, ain't you?

[laughing, Tombs advances toward Tree, who lies helplessly on the floor]

Joseph Tombs: [laughs] That's right, crawl, little girl, crawl... don't worry, I'll just make this real quick for ya, OK?

[Tree is overwhelmed with fear. Suddenly, her watch beeps. To Tombs' surprise, Tree smiles confidently. The lights go out for a few seconds. Once the lights are back on, Tree has disappeared from view. Tombs is confused, unaware that Tree has retrieved the gun and stands behind him]

Tree Gelbman: Hey!

[Tombs turns back, facing Tree, who points the gun at him]

Tree Gelbman: Safety's off. Thanks for the tip.

[without hesitation, Tree shoots Tombs three times. The serial murderer collapses to the floor, dead. Tree sighs in relief, believing incorrectly that the time-loop is resolved - unaware that she has yet to deal with the main culprit]