Not only what what made Annie different from other grad students on Tuesday, but what made her different from ALL the grad students he had interacted with in the past few years? Maybe getting engaged and living with his fiance made him exceptionally sensitive toward a happy, vibrant, secure woman. Wonder what was going on in raymond's life/mind that had recently changed?
these are two different questions you are asking, IMO
1) what made Annie different? (in RC's mind)
and
2) what was going on in RC's life/mind that had changed?
We'll never know the the answer for either question for sure, since they involve getting in someone's head. (and, as we've said, it's dark in there.)
But the answers
might just intersect at the wedding stuff.
Also, when you look at things that way, it swings us back to more of an infatuation motive. Most guys don't give a rat's arse (pardon the pun) that a chick at work is getting married. Maybe RC
was bothered by it.
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Changing directions, and looking at question 1)
Another way Annie might have been different in RC's mind:
If she really was having a problem with regard to the mice, and she really did mess things up and/or ignore/break protocol. Which RC cared about deeply.
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And yet another angle, to look at question #2):
What had happened recently to change things for RC:
If Grad students were complaining about RC, and RC realized that was happening, perhaps RC had been rebuked by authority. Perhaps he felt his job was threatened via these complaints.
Then, it may not be about Annie so much, but about the fact that she was simply the next grad student who walked in, or messed up. And he was ripe for an escalation.
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okay, thank you eyes4crime. now my brain hurts a little, though.