Which is the only snake species that actively builds a nest structure to lay and guard its eggs?

Introduction / Context:
Reproductive behaviour is an important topic in animal biology. Most snakes simply deposit their eggs in a safe, warm place or give birth to live young, with little or no parental care. There is, however, one famous exception: a snake that actually builds a nest to protect its clutch. This question asks which snake species is known for this unique nest building behaviour.

Given Data / Assumptions:

• The question focuses on nest construction, not just choosing a hiding place.
• The options list Viper, King Cobra, Anaconda, Python, and Rat snake.
• The correct species gathers nesting material and may guard the eggs.
• Only one of these snakes shows this advanced parental care.

Concept / Approach:
The King Cobra stands out among snakes because the female assembles a nest out of leaves and vegetation. She lays her eggs inside and often remains nearby, guarding them for a period. Other snakes may lay eggs in burrows, hollow logs, or under rocks, but they do not intentionally build a nest structure. Some pythons protect their eggs by coiling around them, which is brooding, not nest building with external material. Thus, when asked about the only snake that builds nests, the correct response is King Cobra.

Step-by-Step Solution:
Step 1: Understand that the key phrase is only snake that builds nests, which implies uniquely documented behaviour.Step 2: Recall that King Cobra females are known to gather leaves and create a mound for egg laying.Step 3: Consider that vipers and rat snakes generally do not construct nests; they simply use existing shelters.Step 4: Recognise that although pythons care for eggs, they do so by coiling and not by building a nest out of materials.Step 5: Conclude that King Cobra is the only species listed that clearly fits the description and select it as the answer.

Verification / Alternative check:
Standard zoology texts and wildlife documentaries repeatedly highlight nest building as a unique feature of King Cobra reproductive behaviour. No similar nest construction is attributed to vipers, anacondas, pythons, or rat snakes. This cross checking reinforces that King Cobra alone deserves this distinction.

Why Other Options Are Wrong:
Option A: Vipers are ambush predators that either lay eggs or bear live young without building nests.Option C: Anacondas are live bearing snakes and therefore do not construct nests at all.Option D: Pythons brood their eggs by coiling around them but do not gather leaf material into a nest structure.Option E: Rat snakes lay eggs in sheltered places but do not engage in nest building behaviour.

Common Pitfalls:
A frequent confusion is between nest building and egg brooding. Many students think that any snake guarding eggs is building a nest, which is not accurate. Others assume that large, famous snakes like anacondas must do so. Always distinguish between simply laying or guarding eggs and actively constructing a nest from vegetation, which is a signature behaviour of the King Cobra.

Final Answer:
The correct answer is King Cobra.