Oh you know how Dave is, he can turn his phone off for days
How come Dave couldn't make it?
Scene 2 (PRESENT DAY)
Who are you I haven't done anything
I don't know who you are
You know exactly who this is and what you have done.
I can't believe you've done this to me
Flashback: Sarah and Alex are eating there lunch together, on a meet up date, when Alex ask on the where about's of Dave, and why he could make it, Sarah shrugs it off saying how they know how Dave can be like at times, and quickly changes the subject
A year on from that day Sarah is on her phone when she gets a mysterious call from her long lost friend Dave saying "I can't believe you've done this to me" and starting to accuse Sarah of doing stuff do him, not knowing how to feel about this she bursts into tears, this therefore could be hinting that Sarah does indeed know something in which has happened to Dave, and therefore she could be guilty of causing Dave harm, and therefore could be hallucinating the calls.
This is where i am going to have the close up of Sarah's eyes crying, this could therefore be questioning , whether she is crying over the guilt she could possibly be having after the year, and therefore makes the audience question whether Sarah can be trusted if she is willing to hide something about one of her closest friends, maybe this could be hinting that if you do bad to one of your friends, they won't let you forget, and therefore will come after you.