Taxing out in SLC at night after about 6 inches of new snow but just light at the moment. Southwest told to follow us but powers up and jumps in front. Ground admonishes them and they say sorry thought you meant other Delta. We are taxing about 10 knots on snow covered taxiway and Southwest Disappears like we are standing still heading to 34. . Suddenly weird cloud of billowing snow and reflecting lights, snow clears for a second to reveal Southwest sliding to a halt, engines in reverse about 70 degrees off taxiway heading. They found the end of the conga line and apparently needed reverse to stop and the engines did not spool up at the same rate! Long pause as they sat cocked 70 degrees off with no one saying anything. Suddenly someone comes up on the radio and says “Now for my next magical trick”!