Talking about Snakes in the Year of the Snake | “Human greed is like a snake swallowing an elephant”, why can a snake’s mouth open so wide?

The idiom "Human greed is like a snake swallowing an elephant" is familiar to everyone. This idiom comes from the legend of "A snake eats an elephant and its bones come out after three years" in the Classic of Mountains and Seas.

Although it is still unclear whether snakes can swallow an elephant, snakes can indeed swallow prey that is much larger than their own heads. Why can snakes open their mouths so wide? How do they digest these huge prey?

Source: 4 volumes of "Li Sao Tu" by Qu Yuan

First of all, we need to understand the unique head structure of snakes. Snakes' mouths can open to amazing angles, which is mainly due to their unique skull and jaw structure.

The snake's skull is made up of multiple independent bones. Unlike the human upper and lower jaws which are tightly connected by joints, the snake's upper and lower jaws are connected by ligaments and muscles. Not only can they be opened up and down, but there are no restrictions in the left and right directions as well, and they have extremely high flexibility.

So, people may suffer from dislocation due to yawning or laughing with their mouths too wide, but some snakes can open their mouths wide and swallow an egg that is larger than their heads whole without dislocation, so there is no need to worry about temporomandibular disorder.

The mandible is connected by muscles and ligaments

Image source: Baicai and Dolby

In addition, the front end of the snake's mandible is not fused, and the two sides can move independently. This structure allows the snake's mandible to open downward very wide, far more than other animals.

When swallowing prey, snakes can open their mouths to a very large angle, even up to 130 degrees (you should know that our human mouths can generally only open to 30 degrees), so snakes can easily swallow "giants" compared to the size of their heads.

After biting the prey, the snake's maxilla, palate, pterygoid, and mandible can alternately pull the food backwards, and the upper and lower jaws move forward to wrap around the food, ensuring that the prey cannot escape.

Now that we know the skeletal structure of a snake's head, let's talk about how snakes can swallow their prey into their stomachs.

The way snakes eat can be understood as "swallowing a whole prey" because snakes do not have the ability to bite and chew, so no matter how big the prey is, they choose to swallow it directly. However, the process of snakes swallowing prey is a complex and orderly physiological mechanism.

Before swallowing prey, snakes secrete a large amount of saliva. This saliva acts like a "lubricant" to help snakes swallow large prey more smoothly. Snake saliva not only acts as a lubricant, but also contains some special digestive enzymes that can initially decompose prey and make it easier to digest.

In addition to saliva, snakes have a lot of teeth, muscles, skin, esophagus, and respiratory systems! Snakes have backward-curved teeth, which helps to hold prey in their mouths and prevent them from escaping.

When a snake starts to swallow, its lower jaw will gradually open, taking the animal's head into its mouth (we snakes are very smart! They will choose to start "attack" from the smaller end of the animal), clamping the animal's body with its teeth, while the muscles and ligaments in the head will work together, relying on the left and right interactive movements of the lower jaw to slowly push the prey into the esophagus.

Why doesn't the snake's skin get torn apart by the huge prey during swallowing? In fact, this is because the snake's skin is extremely elastic. Its skin is covered with loose connective tissue and can stretch with the size of the prey without tearing.

At the same time, the snake's ribs and organs will expand with the body and adjust their position in time when needed to provide more space for prey.

The snake's esophagus is also specially adapted for swallowing prey. It is extremely stretchable and can accommodate a much larger volume than usual. The walls of the snake's esophagus are made up of strong circular and longitudinal muscles that constantly contract to push the prey into the stomach bit by bit.

This peristalsis allows even large prey to be swallowed whole, and the lining of the esophagus is able to expand considerably, stretching along with the skin and body to accommodate the size of the prey.

The process of swallowing prey by snakes may last for several minutes or even hours, depending on the size of the prey and the species of snake. In order to survive better, smart snakes have also mastered the skills of avoiding suffocation by blocking the trachea when swallowing prey during the long process of evolution.

The snake's tracheal opening is located at the base of the mandible, and when swallowing, they can extend the trachea outward to the side of the mouth, allowing them to continue breathing while the prey occupies the mouth, ensuring that breathing is unobstructed and avoids being blocked by prey.

This anatomical feature

Ensures the safety of the snake when swallowing its prey

After swallowing food

The diameter of the snake will be more than doubled.

Green anaconda swallowing a capybara

Image source: Guokr Nature

After finally getting the "meal" into the snake's stomach, how can the snake digest this huge prey? The rest of the work depends on gastric juice. When the prey enters the snake's stomach, the digestion process begins immediately.

The snake's stomach secretes a large amount of gastric acid and digestive enzymes. These gastric acids are extremely acidic (even stronger than human gastric juice), which can quickly decompose the skin, muscles and internal organs of the prey, and even some of the prey's bones can be dissolved.

For example, the bones of small animals will completely dissolve in the stomach acid, converting them into calcium and other minerals that the snake can absorb.

However, for some large animals' hard bones or hard feathers and hair, stomach acid may not be able to completely decompose them, and these parts will be compressed into clumps and eventually excreted through excrement. Gastric juice also contains enzymes such as pepsin, which breaks down the protein of prey, and lipase, which breaks down fat.

The prey is broken down by gastric juice and enters the intestine, which is responsible for further digestion and absorption of nutrients, including protein, fat and minerals.

Unlike humans, snakes can obtain a lot of energy from their prey each time they hunt. A large meal can provide snakes with energy reserves for weeks or even months, reducing their frequency of foraging. Moreover, snakes are cold-blooded animals with a low metabolic rate. After hunting, they can enter a long state of dormancy and concentrate on digesting prey without frequent activities.

Snakes' ability to swallow and digest is a unique adaptation mechanism given to them by nature to help them survive in the wild. Although the "snake swallowing an elephant" is just an exaggerated legend, it vividly reflects the snake's magical physiological structure and strong survival ability.

Author: Hu Xinyue

Editor: Dong Xiaoxian

Reviewer: Zhang Chao, Li Peiyuan