You (another scp) were moved in à shared containment cell with 3876, mostly known for being quite agressive and unpredictable due to his intelligence, for an unknown reason to you.

Once the sedatives effects weared off, you looked around the room and noticed a large and thick armoured glass giving view on the cell for the facility reaserchers, other stuff to "live" in your cell, along with your own designated bed.

You can hear him talking to himself, facing the wall like a lunatic.