The bus charges for the curb like a perturbed elephant. It squeals and stops in front of the line of people waiting to board. I take my turn up the steps and watch my Metrocard slide into the valley with a whir. I grab it when it's spit back out.

I take a seat behind two small children, a boy of about four and a girl who looks two. They are brother and sister, wiggling and giggling as everyone else sighs. It's another hot day. It's only 2:00, and our collective feet hurt. The children's mother stands in the aisle and adjusts her heavy African garb before the bus lurches forward.

Outside, people sweat and try their best to run everyday errands. Some girls strut on the street; some boys are lifting dumbbells in front of a bodega. The brother and sister in front of me are oblivious to anything beyond their two seats of velour upholstery, crushed and darkened under millions of behinds before them. The little girl bats her eyes at the little boy who tickles her arms. Their mother looks out the far window wistfully, like she's trying to find who she used to be.

The little girl throws back her head and laughs, tiny pink tongue peeking out like the petal of a budding flower. I watch intently, marveling at the innocence.

Then the little boy leans forward abruptly and rubs his tongue against his sister's. I'm more than a little shocked. The little girl looks surprised, too, but pleased. She opens her mouth wider, and her brother caresses her tongue with his. Again.

I look at the mother, who is still looking for herself or something. I look back at the children and they are essentially making out. The little boy has instigated it and continues to lead. He cups the little girl's face and gives her lingering open-mouthed kisses, licking and sucking on her tongue.

My studies in human sexuality have taught me that we are all sexual, no matter what society would like to believe about the very old and the very young. Many people report that their first sexual experiences are with a family member in a play situation. Nonetheless, I feel like maybe I should intervene in the hanky panky. These kids are making memories they're old enough to recall repeatedly...during those difficult years when they get bizarre pangs to make out with people they're not related to.

I have a lot of questions, the biggest being "Where did the little boy learn this stuff?" What is he watching on tv? Or does his mom model her kissing prowess at home in front of him? (With that modest dress, who'd have thought)? Or maybe the little boy is a child prodigy who reads and absorbs any piece of literature he can get his hands on, and he happens to have access to Cosmopolitan. Should I be glad they don't appear to have too many problems with sibling rivalry?

I am hot (temperature-wise) and yes, bothered (disturbed, gouge-my-eyes-out-wise) when my stop comes. I vow to stay off public transportation as long as I can, misplacing my metro card in the jumbled chastity belt that is my change purse.