And statement?

In my game I have a script that when I hit mouse 0 (left mouse button) I crouch using this script:

function Update () {
if(Input.GetKey("mouse 0")){
animation.Play("crouch");
}
}

And now when I hit left mouse button, I crouch, but now I want it so that I crouch and as I am crouching If I move forward I crouch walk (I have that animation) How would I do this? thanks!

Add a toggle that is set to true and test against it.

private var isCrouching : boolean = false;

function Update () {
    if(Input.GetKey("mouse 0")) {
        isCrouching = true;
        animation.Play("crouch");
    }
    if(Input.GetKey("W") && isCrouching) {
        animation.Play("crouchWalk");
    }
}