Kissing my sister

So my sister recently split from her boyfriend and had to move back in with me and our mum. Our mum normally goes to bed at 10pm and me and my sister will watch a film before we go to bed. A few nights ago, we were watching the 2009 remake of Friday the 13th when the sex scene started. We were sat next to each other and at one point, we both looked at each other. Next thing I knew, we were making out. After we finished making out, we both composed ourselves and I went to bed but I haven't stopped thinking about it since and we haven't spoken about it either.