This is why I miss my on-sabbatical colleague when he's off campus:

Him: "There are these organisms, cnidarians, that eat algae but don't digest the chloroplasts. They incorporate them into their tissues; they're called kleptoplasts."

Me: "Oh, that's cool...so what percentage of the cnidarian's energy budget comes from the kleptoplasts?"

Him: "I don't know - but zooxanthelle in coral can contribute up to 90%."

Me: "So, theoretically, you could bioengineer an animal that was entirely photosynthetic..."

It led up to this:

Me: "Okay, let's get this straight - we could make a photosynthetic chihuahua that would never need to eat, would never poop, could make oxygen for us, and would move a lot slower and be a lot mellower."

dammit, I want my photosynthetic chihuahua. (My original suggestion was a photosynthetic pig, but I like the idea of a photosynthetic chihuahua better).

I MISS that kind of humor - that kind of just totally outrageous shooting-the-bull where you go on those kind of thought-experiments and you don't regard the impossibilities (not to mention the ethical sticky wickets) of such a venture.