Understand the physiological response to low hemoglobin.

Low hemoglobin means the blood cannot carry enough oxygen to the body's tissues. This state of reduced oxygen delivery is called hypoxia.

When the kidneys detect hypoxia, they release a hormone called erythropoietin (EPO). This hormone travels through the bloodstream to the red bone marrow.

The red bone marrow is the primary site of red blood cell production (erythropoiesis). Erythropoietin stimulates the stem cells in the red bone marrow to increase the rate of red blood cell formation. This increased production aims to raise the overall hemoglobin level and improve oxygen-carrying capacity.

Your answer correctly identifies that the red bone marrow is stimulated to produce more red blood cells as an effect of low hemoglobin.

The final answer is $\boxed{\text{Red bone marrow is stimulated to produce more red blood cells}}$.