This is my argument on pigeon impossible. Here are my reasons on why it's not the pigeons fault.
The brief case was really high tech, so why was it in town? Secret Agent Walter Beckett threw the donut away for the pigeon but since he threw the donut in the direction of the brief case the pigeon accidentally tumbled into the case and got enclosed. Why did Walter have the case open? Someone busy on the phone could've sat on the brief case and broken it. Walter should be more responsible, and keep things a secret (it's in the name).
The pigeon was curious. Walter can't blame him because pigeons don't go to school. The buttons were flashing and making sounds so the pigeon was stimulated. All pigeons do all day is scavenge and eat crumbs off the street, so flashing buttons to him is the best thing since cake! He was having fun you can't blame him for having fun. The pigeon probably wanted to find out what the buttons did, because there were millions of them, he might of thought one of them made super duper lickity cake. Or maybe he wanted a breathtaking story to tell his brothers when he gets home to the nest.
In this argument I was writing from the pigeons point of view. I hope you see where I'm coming from and agree with me.