How do you weapon slide in Gears of War 2?

after all the updates. im asking this because i played a public match clearly on of the guys on my team was a 100 rank and glitched it. now he goes to pick up a weapon slides it and leaves me amazed. i ask him about it and he admits in to doing it i ask him can you tell me how he says no. the time and date i played this game was at 11.50pm 6/8/09 the guy who weapon slide gb name is pozosjessie SOMEONE PLEASE HELP ME I WANT TO KNOW. i have tried youtube and googled it and have not found anything.