NASA cannot bring birds into space because birds need gravity to swallow.

Birds may give a huge “screw you” to gravity as they soar through the sky, but nonetheless good guy gravity is actually the reason they’re alive! In many birds, the esophagus is just an empty chute (it doesn’t contract or push food down in any way).

This is why swallowing for a bird largely consists of lifting its head with its beak pointed up, and letting gravity pull the food down. NASA has stated that this is the reason that birds cannot be brought up into space. Other species have similarly strange way of swallowing:

• In fish, getting food to the back of the pharynx is helped by pumping water in its out and out of its gills. 
• Snakes swallow by raking the lower jaw until the prey is far enough back to be crushed by body undulations.

Swallow some more out-of-this world info from the source! 

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