First of all, buffalo's lungs and heart are bigger than other mammals. This enables them to inhale more oxygen and deliver oxygen to all parts of the body more effectively in the blood.
Secondly, buffalo's nostrils are located on the top of their heads, which allows them to exhale and inhale gas through their nostrils without raising their heads when they are in the water. This posture allows the buffalo to breathe underwater and maintain a stable posture.
In addition, buffalo's nose and ears have closable valves, which can prevent water from entering the nasal cavity and ear canal and keep breathing smoothly.
Finally, buffaloes are buoyant and easy to float on the water. This buoyancy helps buffalo to save energy and reduce energy consumption in water.
To sum up, buffalo can hold their breath in water because their lungs and hearts are big, their nostrils and valves are special and their buoyancy is good. These characteristics enable buffalo to adapt to the underwater environment and survive in the water.