My response without having read the other comments yet:
Have to admit that I missed a couple of the "slash/slice" references in #2. Not reading closely enough!
What would I do next? I was waiting for more to be revealed, not guessing.
The dialogue seems odd and unlifelike.
"Can I help you?" is not something I would say to an intruder, nor would I explain that I was "moving stuff." And what exactly is she moving, and is she doing it all alone?
The man's response sounds lame in the extreme and not in keeping with the way he just walked into the house, looked over the possessions on the table (like a burglar), and started playing with the boxcutter. (If there is going to be blood and gore, by the way, I'm out of here.)
Then the woman, instead of being glad that he is leaving, stops him with a question? Does she recognize him from the neighborhood? Why would she want to prolong a conversation with a stranger in her house? The whole conversation seems very odd.
Having read and watched lots of murder shows, I am suspicious of this man and think that he is "faking" his behavior of innocence. He wants the woman to think that he is not menacing. She gives him an "out" by suggesting that he might be a neighbor. Basically, this offers him an invitation to stay. We don't know if she has any sort of "bad feeling" about this stranger in her home.
The man could have picked up any of the items he found. He could have taken the keys and left, only to come back later. He could have stolen money or credit cards. Handling the box cutter is certainly ominous - a weapon to slash with.