Sometimes there are things about your roommate that you don't bother to question. Sometimes there are things that they don't question you about.
It just works better that way, and besides... everyone is different.
When I came home a while back... there was a small tin-foil type pan in our oven. It looked like it was being used as a drip try (which is smart, because I hate cleaning the oven) but for the most part I found it was in the way. Each time I cooked, I'd take it out of the oven and put it on the top shelf. Then, when I was finished, I'd stick it back in.
Roomie got a cast iron pan that needed to be seasoned, and she'd read about seasoning inside the oven, so she decided to give it a try, the little tin pan served it's purpose as a drip tray, and the next day as we started to cook, she took it from the oven and said "I hope you don't mind, I'm going to throw this out so the apartment doesn't smell like oil".
"I don't mind" I said... and then I added.... "it's not mine... I thought it was yours"
she looked at me strangely... and we both started to laugh... not knowing where the pan had come from... and then we realized... it had belonged to the girl who stayed in my room when I went to Togo two years ago! We've both been taking it out of the oven each day, and putting it back, not questioning it's purpose....
I wonder how many other things in our life are like that?