Tyler Dahle

Headphones can be a very strong indicator of 'nobody talk to me...' and 'returning a smile' is just her being polite if the OP smiled at her first. I know nothing annoys me more than people attempting to talk to me while I have headphones in to just small-talk garbage. That is the reason I have headphones in!!

I find it odd that so many people are against a harmless little lie about what ailed you... Nobody can actually ever find out what it was you were out of the office for, so how can telling them you had a terrible headache or something ever 'come back to bite you'. But I don't get migraines or headaches on any regular basis, like you, but I have had a random stress headache attack that left me incredibly nauseous and bedridden for a few hours, so they can definitely just come about, especially if stressed!

I believe it was in the 4th book that Mad-Eye mentioned how everyone in class could point their wands at him and say Avada Kadavra and he would only get a nose bleed because they wouldn't have the intent/power to back it up. Going with Arcanist Lupus's comment, it could be the wand wouldn't kill its TRUE owner, and kinda botched the killing curse for Voldemort.