This is a true story that might inspire some playful activity or erotic writing.
Last year I had a married female friend over to visit. We are secret “friends with benefits”. After a nice morning encounter in which I ejaculated on her neck and chest she did a quick cleanup and headed out to meet some family members for brunch. Later that day she texted to tell me that she was sitting with her family at the restaurant and felt the need to scratch a patch of dry skin on her lower neck. It was only when doing so that she realized she was scratching off a couple of drops of my dried semen that she had missed during her earlier cleanup. She said it appeared none of her siblings noticed, but she wasn’t completely confident about that. At least nobody mentioned it. In retrospect she thought it was quite funny and I almost suspect she might try it again, but intentionally.