Ever Wondered Why The Central Perk Couch In 'Friends' Was Always Free?

You may think that you know every single episode of Friends inside and out, but we bet you've never noticed THIS in the hit series.

Ever wondered why the sofa in Central Perk is (nearly) always free for Monica, Rachel, Joey, Phoebe, Ross and Chandler?

Well, thanks to Tanya Ghahremani at Bustle, it's come to our attention that it's all down to one simple sign. No, really.

Once you've spotted the 'Reserved' sign on the coffee table, it's kind of hard not to spot it in every single episode.

Like this one.

Even in this one, where it's propped up against the napkin dispenser.  
Ah, salmon skin roll.