Why do you get that feeling when you look into someones eyes?

Dos anyone else get that feeling,when they look into people's eyes like in their stomach? Its kinda like butterflies?
Not only when looking into a specific person's eyes,its anyones.
What is it? Why does it happen?

I only get that feeling when I catch the eye of a guy I like

but I have no idea why

I feel awkward when I look into someones eyes !
but when its my girlfriend's eyes I just feel peaceful .
but I don't know about you .

It's either Lust, or Love. You choose which.

They say eyes are the window to the soul, you can read so much about a person in their eyes.

Sometimes, I don't think it's just a person's eyes that give you those "butterflies," but more less the way the eyes look when they're looking back at you. They give you that certain "look," the glint in their eye is just at the right angle, the glossy/glaze over their eyes kind of lets you know what they're thinking. Their eyelids, by how much they cover, shows you what kind of mood you're in.

That's what I think, You can read a person by details that the eyes offer. I think you know the answer to your question, the "butterflies" come from eyes that show infatuation.