KeyDown -> Animate once and pause?

Hi, I have a model with a single animtion of 10 frames. What im trying to do is, whilst a key is held down (which does other stuff) it playes the animation until the end and then stop and stays on the last frame and then when i let go fo the key it reverse the animation back to the start?

Now I thought I had cracked it when I found clampForver but I noticed the longer its "clampedforever" the long it takes to reverse the animation? Is time still going on after its got to the last frame? I dont quite understand?

This is my current code... (c#)

Code (csharp):

1. if (Input.GetKey ("b")) {
2.                 if (!myObj.animation.IsPlaying("ani1")){
3.                         myObj.animation["ani1"].speed = 1;
4.                         myObj.animation["ani1"].wrapMode = WrapMode.ClampForever;
5.                         myObj.animation.Play ("ani1", PlayMode.StopAll);
6.                         }
7.                 }
8.  
9.         if (Input.GetKeyUp ("b")){     
10.                 myObj.animation["ani1"].speed = -1;
11.                 myObj.animation["ani1"].wrapMode = WrapMode.ClampForever;
12.                 myObj.animation.Play("ani1",PlayMode.StopAll);
13.                        
14.                 }

Hope you can advise.
Thanks
Andy