The drop rate of this pet is roughly 0.1% (one in every thousand kills) and takes an incredible amount of patience and determination in order to get one. Due to the difficulty of obtaining one, and thus their rarity, they can sell for fairly large amounts of gold on the Auction House, at least as far as pets are concerned. The table below shows the cumulative probability of getting at least one after a number of kills. Mall:1-1000drop
The phrase "Still flying..." in the tooltip is a reference to Joss Whedon's series Firefly. The spaceship in the series is of the Firefly model, and after a terrible day, the Captain of the ship observes "We're still flying".