Concentration

Breath hisses like a burning log.
The cracked black wood burns red,
smouldering in a deep iron heart.
Too much air, it flares and flickers out.
Too little, it starves and we get cold ash.
But when the grate is open well enough
it breathes hot and constant.
Sometimes a blister, a spark, a crack.
Mostly nothing but silent, black heat
warming the room without display or cease.