为什么大便的时候会流泪，感冒时也会留液？这似乎是一个令人费解的问题。事实上，这种现象与我们身体的神经反射机制有关。下面我将为您详细解释这个问题。

在我们排便的过程中，可能会出现泪水的流出。这是因为我们的眼睛和鼻子之间存在着一条称为泪液引流通道的管道。当我们用力排便时，腹压增加，同时通过膈肌的作用，压迫到位于鼻腔和眼睛周围的面神经。这会刺激我们的面神经，导致泪液引流通道打开，使泪水从眼睛中流出来。

Why do tears flow during bowel movements and nasal discharge occur during a cold? This seems to be a puzzling question. In fact, this phenomenon is related to the reflex mechanism of our body. Below, I will explain this issue in detail.

During the process of defecation, tears may flow out. This is because there is a drainage channel called the tear drainage pathway between our eyes and nose. When we exert force during bowel movements, the intra-abdominal pressure increases. At the same time, due to the action of the diaphragm, the facial nerve located around the nasal cavity and eyes is compressed. This stimulates our facial nerve, causing the tear drainage channel to open, allowing tears to flow from the eyes.

当我们感冒时，鼻子会有充血和分泌物的产生。这是因为感冒是一种上呼吸道感染，病毒侵入我们的鼻腔和喉咙，导致炎症反应。充血的鼻黏膜会刺激我们的鼻腔神经，引起鼻涕的分泌。另外，由于上呼吸道感染引起的炎症反应，也会刺激我们的面神经，引起泪液引流通道的打开，使泪水从眼睛中流出。

When we have a cold, the nose becomes congested and produces secretions. This is because a cold is an upper respiratory tract infection, and viruses invade our nasal cavity and throat, leading to inflammation. The congested nasal mucosa stimulates our nasal nerves, causing nasal discharge. In addition, the inflammatory response caused by upper respiratory tract infections also stimulates our facial nerve, causing the opening of the tear drainage channel and tears to flow from the eyes.

值得一提的是，大便时流泪和感冒时流涕并不是所有人都会出现的现象。这取决于个体的生理特征和反射神经的敏感性。有些人可能更容易在排便或感冒时产生这种反应，而另一些人则可能没有这种感觉。

It is worth noting that not everyone experiences tearing during bowel movements and nasal discharge during a cold. This depends on the individual's physiological characteristics and the sensitivity of the reflex nerves. Some people may be more prone to this reaction during defecation or a cold, while others may not experience this sensation.

总而言之，大便时流泪和感冒时流涕是身体正常的生理反应。它们是由于神经反射机制的作用导致的，当我们用力排便或感冒时，这些反射被触发，引起相关的液体流出。

In conclusion, tearing during bowel movements and nasal discharge during a cold are normal physiological responses of the body. They are caused by the action of the reflex mechanism, and when we exert force during defecation or have a cold, these reflexes are triggered, resulting in the flow of the respective fluids.

Note: The English translation provided is a direct translation of the Chinese text and may not reflect natural English syntax or grammar.