[Guest]

I bring pleasure

I take pain

Expand I do

And contract again

[Guest]

And that's how I wanted it. I wanted you to think, "The answer is so easy, that the answer couldn't be the answer. It must be something else."

I think most riddles are like that, anyway. At least the ones I get wrong

[Guest]

Umm, am I missing something here? Because I was pretty sure I had it when I first read the puzzle.

******

It can give a woman (and us men) great pleasure.

It takes an extreme amount of pain during child birth.

It expands when filled or aroused.

It returns to it's original size when not filled/aroused.

[Guest]

I know the OP has already declared the correct answer, and L.I.S. has stated "...pick a body part...", but another answer that fits very well (and is close to crossing the line) is...

colon or sphincter

[Guest]

At first I thought it was smile, then as you said it was a body part I thought it was the iris of the eye.

I bring pleasure

I take pain

Expand I do

And contract again