What is 'stretched'?
This glitch is only doable in Halo 2 multiplayer, when one is playing as a Spartan. It causes the neck to stretch, or sometimes makes the body flop. To do this, go onto the map Midship, and find one of the shields.
Crouch down and keep walking towards the shield, so you don't bounce away. Get somebody to 'assassinate' you. If you do this right, the Spartan's head should go through the shield with the body on the other side. The shield makes the body pull away, but it can't because the head stops it from doing so. This causes the Spartan's neck to stretch like a rubberband. Sometimes it flops around like a fish out of water. Also in Halo 3, when a player dies and hit something violently, theres a high possibility they stretch, but it only happens for a split second.
Also See
Hollywood Halo-neck stretch glitch[1]