We cry when we yawn mainly because the facial muscles around our eyes contract and put pressure on the tear-producing glands, called lacrimal glands. This muscle contraction squeezes out tears, causing them to spill from our eyes during a yawn. Additionally, the contraction can temporarily block the normal drainage of tears, so tears accumulate and then flow down the cheeks when the muscles relax after yawning. Another contributing factor is that yawning may help cool the brain, and tear secretion could be a part of this cooling mechanism. Also, if the eyes are dry or tired, yawning can trigger tear production to moisturize and protect the eyes. Thus, a combination of muscle pressure, tear drainage blockage, and eye lubrication needs explains why eyes water during yawning.
