At 7:25 p.m., a few witnesses saw the fabric ahead of the upper fin flutter as if gas was leaking. Others reported seeing a dim blue flame – possibly static electricity, or St Elmo's Fire – moments before the fire on top and in the back of the ship near the point where the flames first appeared. Several other eyewitness testimonies suggest that the first flame appeared on the port side just ahead of the port fin, and was followed by flames which burned on top. Commander Rosendahl testified to the flames in front of the upper fin being "mushroom-shaped". One witness on the starboard side reported a fire beginning lower and behind the rudder on that side. On board, people heard a muffled detonation and those in the front of the ship felt a shock as the port trail rope overtightened; the officers in the control car initially thought the shock was caused by a broken rope.