I remember one time having sex with my GF in University back at my parent's place.
My ex GF was 6' tall, so we regularly had sex standing up. This was one of those occasions we did it on the quick standing up in my room with the door open so we could hear if my parents came home.
Just after we finished, we looked outside the door and the cat was sitting there staring at us and her eyes were as big as a couple of loonies. My ex burst out laughing and I would have sworn the cat was overwhelmed with what she had seen.