ya the zipline isn't really a trap the traps main purposes are to kill zombies the zipline is more of a means of escape (or glitching lol) u can kill zombies with it but it's not a trap if ur trying to get the achievement u activate 2 electric barriers and the flogger or 3 barriers if u have the time easiest i think to start the round in dr.quarters with tht barrier on then run and turn on the flogger and go thru it and activate the fishing hut barrier i don't even think u can get the achievement by killing one with the zipline