Answer:
It is weightless, you can see it. If you put it in a barrel it will make it lighter?
In we go, out we go. All around and in a row. Always, always steady flow. When we'll stop, you'll never known. In we go, out we go.
I am the hole in the night, the ever watchful eye. I return in a cycle, to enlighten the sky.
When liquid splashes me, none seeps through. When I am moved a lot, liquid I spew. When I am hit, color I change. And color, I come in quite a range. What I cover is very complex, and I am very easy to flex.
I tremble at each breath of air, and yet can heaviest burdens bear.
This food is a tortilla filled with cheese and sometimes chicken before being heated or cooked.