The side arm is used for the mouthpiece. You sort of feel like 007 in the movie Thunderball using the breathing device to escape the shark pool. I find it more comfortable to hold the iHeat at 90 degrees to your mouth rather than perpendicular to it. All of the particulate matter that does make it to the end of the test tube, stays below the silicone sleeve. It creates a distinct dirty/clean line. I'm really enjoying the new cooling tube with the iHeat, Lil' Bud, and Heat Island.