the small room , with its panelled paper walls and tatami mats , was adorned with only three features : a small cavity in the floor by the far left corner , in which stood the kama , an iron kettle , simmering silently upon smoking hot charcoal ; to the left of this , the mizusashi , a water container for topping up the kama , whilst in the opposite corner stood a short , wooden table of about six inches in height called a tokonomai , on which stood a plain , porcelain vase .