I recently watched an episode of "Elementary" where the bad guys were communicating through carrier pigeons, and that is why there was no trace or record of any connection between the two. I thought it was pretty clever.

So my idea is simple:

1. Make Pidgeon Mob. Killing it gives a chance to get 0-1 feather. with 1 EXP drop. (Animated wings? :3)

2. Be able to tame pigeon using Seeds.

3. Make Pidgeon GUI when tamed and right clicked, have 2 Slots available, 1 strictly for a written book, and one for any one item (Can't Stack), Gui should also have A behavior modifier, like "Stay", "Follow" (Name input) and "Fly to" (Name Input), Difference in follow and fly to is fly to will fly back once its items are taken, and follow is to constantly be following them. "command" the bird (Name input List) only editable by owner.

4. People can stun birds by using arrows. (Arrow does no damage when unstunned, when stunned, yes. Flame I will still affect it even if unstunned.) Swords or brute force will just kill it. Birds will be stunned for approx. 30 seconds, then get up and continue whatever it was performing, or try to run if there is danger.

5. Birds will travel a steady speed, and fly over or around any obstacle. Stays about 7 blocks above and away from anything in its path during flight. Flying down a slope gives it a slight speed increase. Over time as the bird completes sending messages back and fourth its speed gradually rises.

6. The birds GUI can be accessed by anyone as long as the bird has an owner. The GUI will present the owners game name inside, as well as its task at hand.

7. The task of the bird can only be set by the owner, and whenever it completes a task it waits about a minute and then instinctively travels back to its owner, if the user it traveled to is on the command list, he can stop the bird from leaving right away, and edit its task.

8. In the GUi you can determine if the task is complete when the left, right, or both slots are empty.

So with this in place, people could secretly message each other from long distances, and the one item slot would make it slow to deliver say 3 diamonds, but it could essentially be used for long distance trading. And since the bird can be stunned, people could intercept the bird. Say if you are in a Hardcore server, and you have enemies. If they plan things right they can intercept your messages, read them, and take items. or even kill the bird if they decide to. I think it would give a great "undercover" feel in the game.