What you never noticed about Rachel and Monica's apartment on Friends.

Monica and Rachel’s apartment on Friends became many viewer’s second home (that’s what it felt like through the TV screen).

Monica and Rachel were an extension of our housemates and we felt like we knew that apartment inside out. But we all missed one vital thing.

We wonder if Monica and Rachel noticed. Image via iStock.

The window in the kitchen of the two women's apartment had an ever-changing backdrop. Sometimes there was a wall behind the window, sometimes there was a black canvas, sometimes a window in the bottom corner and on a few occasions, there was a beautiful view of the city.

So either someone was busy building walls and knocking them down again, or there was a bit of a slip up on set some days.

Here's the window in it's array of scenes (Post continues after the gallery)...

We have watched Friends a thousand-billion-trillion times and sat inside that kitchen, gazing at the window on many-a-weekend and week night.

Yet we failed to notice the changing backdrop.

We were too busy being embroiled in the Friends hilarious dramas and antics to notice.

Did you notice the changing apartment window?