My sister practices her oral skills on me to better please her boyfriend

My sister has been practicing her oral skills on me, not because she's into incest, but because she wants to please her boyfriend better. She's always been a bit of a prude, so it's been a challenge for her to get good at giving head. I've been more than willing to help her out, even though it's been a bit of a turn-on for me. Today, after a week of not seeing each other, she came over and we got down to business. She's definitely improved, and I can tell she's getting more into it. After a few practice runs, she finally made me cum. She was surprised when I came in her mouth, but she swallowed it like a good girl. I guess practice makes perfect. Now she can go back to her boyfriend and show off her new skills.