I feel very tempted to sniff my sister's used undergarments.
What do you think is causing you to feel this temptation.
It smells good and makes me feel loved.
You shouldn't take your sister's things. That's gross to sniff her underwear. That's really disturbing.
What's so disturbing about it?
Well it is your sister. The only reason why you would ever sniff someone's underwear would be that you think it is attractive. You should probably keep from doing that as your sister may find it to be disturbing if she finds out.