Are you saying it’s an old saw?
Uncooked rice?
Oh yeah, this. Don’t birds explode when they eat rice, and exploding birds are a common event on weddings?
I don’t want to get sidetracked by a tangent about what is or isn’t lateral thinking or a pun. Nevertheless, I stand by my original post that this question is a riddle which has a trick answer, and not a puzzle which can be solved by logic.
Here is a similar story which is a puzzle solvable by logic. The answer seems pretty obvious to me.
After the prisoner is convicted, his sentence is determined by an ordeal. The rule is that the king puts 2 pieces of paper put in a hat. One paper says “freedom,” and the other says “death.” The king hates the prisoner, so he puts in 2 papers that both say “death.” The prisoner chooses a paper, but the king gives him his freedom. What did the prisoner do?
Here’s my guess:
He chooses a piece of paper and hands it to the king, and tells the king that he wants the opposite of what’s on the paper?
He eats the paper and says it must be whatever the other paper isn’t?
I have to admit, I’m amenable to the like of the very first reply: the guards are prepared to behead him if he beheaded it, or stomp him to death if he stomped it to death, and he explains that he — killed it by tearing its wings off, at which point they stare blankly.
BINGO!
Nope. The exploding bird thing is urban legend and has been frequently contested by ornithologists. Rice is (mostly) harmless to birds.
The biggest problem is that most white rice has little nutritional value, which means you might end up under-nourishing the bird.
But migrating birds will often eat rice and they don’t have any issues.
Caffeine, though. That’s a bitch for many animals. Dogs and birds included, which is why you shouldn’t feed chocolate to either.
Chocolate is poisonous to dogs mostly because of its theobromine content, which dogs are unable to metabolize effectively. Although I don’t suppose the caffeine content does it a whole lot of good either.
-“BB”-
Well, there’s your solution. He feeds it a reasonable amount of rice every day until it dies.
My first response in this thread implied as much, but I was figuring chocolate flat out which will kill the bird far faster than under-nourishing it.
But the OP said we’re not allowed to assume facts not in evidence.
Which is why my second response referenced 14 k of g in a f p d.
I have a feeling that just like that one, this riddle isn’t going to have an answer.
Just for the record, I knew this, and my question was tongue-in-cheek. 
Question: What is seen in a mirror when it is face-to-face with another mirror?
Who is looking?
I would take one paper, eat it, and claim that it stated the opposite of the remaining paper. As the remaining paper says “death”, the one I ate must have said “freedom”.
ETA: Ninja’d by Ulf_the_Unwashed by a ton. Only read the direct replies, sorry.