If the survivor is already in the goo the achievement won't pop. When the Spitter spits and if it hits the survivor move him out of the goo then pounce with the jockey and steer him into it. Keep an eye out for the Spitter with your jockey, they will be highlighted in blue kind of helps to have full subtitles on. Then as the survivor go grab that gas can then go wait towards the left rear of the car, kind of by a pillar as well. Restart until you spawn as the jockey, set up your jockey behind the first pillar, a little ways before the lone gas can on the first floor.
main account as infected, 2nd controller as a human. Start up a scavenge game on Dead Center in the atrium. IMPORTANT NOTE: once you spawn the Jockey at the start of the match and if you don't get the achievement on the first try just hit rematch on both controllers and you'll spawn they jockey every time at least that's what happened for me. With the new update there can now be more than 1 special infected.
With the new update that was released on 4/20/10 this achievement can be earned in Scavenge mode by yourself as long as you have 2 controllers.
