Despond

Desponds are creatures that feed off hope. They resemble dogs, but have three legs and a tendril that protrudes from its mouth that clings to people's throats. They also have razor-sharp teeth. The tentacle, when stuck to throat of a person, sucks the hope away. These people now despair and claim that there is no hope of escaping.

In Terminal 4000, there are thirteen Desponds in all. Because of their presence the terminal was closed down and so no transport was taken to the location because it was too dangerous. The Doctor loses hope after being fed on, and Amy is forced to help him. (NSA: Terminal Of Despair)