Snurgle

The Snurgle is an enemy in Spirit Tracks which resembles a small blue and yellow flying elephant. It can only be found while riding the Spirit Train across Hyrule. These beasts will fly around the train for a few seconds before trumpeting and thereafter swooping in for an attack. Link can blow the train whistle to temporarily stun Snurgles or fire the cannon to shoot them out of the sky. A single shot with the cannon is all that is required to defeat one. If the train is carrying cargo, such as fish, a Snurgle will attempt to steal the cargo instead of attacking the train. This bothersome act occurs when Link is trying to transport 15 fish to a woman in Hyrule Castle Town to receive a Force Gem.

Snurglar
A Snurglar is a large, red variety of Snurgle that appears only in the Fire Realm. In his quest, Link must stun three Snurglars to gain access to the Fire Temple, as they each hold a key needed to unlock its front door. The Snurglars, as hinted at by Gorons in Goron Village, are sensitive to loud noises such as the Spirit Train's whistle, however, only to a specific rhythm of such noise: one short toot, followed by one long toot. This special whistle will freeze the Snurglar in their tracks, like their smaller counterparts, allowing Link to pound at it with a shot from his Cannon. Unlike Snurgles, the cannon explosions will not defeat these large beasts, but will knock them unconscious for a bit; upon coming around, the Snurglars without keys will follow and hone in on the Spirit Train if it is nearby, in an attempt to retrieve their keys. Unlike Snurgles, there is no true way to defeat these enemies save for knocking them unconscious and leaving the area. Once all three keys are secured and the Fire Temple complete, the Snurglars are never seen again, and in their absence their Snurgle counterparts will infest the Fire Realm, as they do with the others.

Trivia

 * Snurglar could have possibly been derived from the word "burglar."