[mehrdadn]

I'm a little confused, why is the second "que" there? Why can't it just be "Qu'est-ce que c'est cette chose-là?"? (I'd expect it to be the equivalent of "What is it that it's that thing there?")

[mratsim]

It's decorative, it has no meaning.

Similarly you have "les choses que l'on voit" and "les choses qu'on voit" with the "l'" being there for prettyness.

[mehrdadn]

Oh huh, merci!