Two siblings, left alone, can't resist the taboo. The boy's little sister, curious and horny, decides to experiment with oral sex. She takes his cock in her mouth, exploring its length and girth. She spits on it, using her saliva to slick up his shaft, before eagerly sucking him off again. He cums hard in her mouth, and she swallows every drop, leaving them both satisfied and sneaky, but with a secret they'll always share.