In this riddle you are asked: "What has a mouth but never smiles?" Which natural feature or thing fits this description?

Introduction / Context:
This is a common riddle that uses a double meaning of the word "mouth." In everyday language, a mouth is part of a face that can smile, talk or eat. However, many natural features are also described as having a mouth, even though they have no emotions. This riddle asks you to identify something that has a "mouth" in this broader sense but can never smile.

Given Data / Assumptions:

• The riddle question is: "What has a mouth but never smiles?"
• We must choose one correct answer among the options.
• The options include a river, a cave, a volcano and a baby.
• We assume the riddle relies on the geographical term "river mouth."

Concept / Approach:
The phrase "mouth of the river" is standard geographical terminology. It refers to the place where a river flows into a larger body of water, such as a sea, ocean or lake. A river, therefore, is said to have a mouth, but it does not have a face or emotions and cannot smile. The riddle takes advantage of this familiar phrase to mislead people who are thinking only about human or animal mouths.

Step-by-Step Solution:
Step 1: Recall that many rivers are described as having a "source" where they begin and a "mouth" where they end. Step 2: Understand that this "mouth" is a metaphorical term, not a literal mouth with lips and teeth. Step 3: Recognise that a river's mouth cannot smile because a river is a natural flow of water, not a living being with emotions. Step 4: Compare this with a cave or a volcano. These also sometimes are described as having an opening, but the phrase "mouth of the river" is much more common and exact. Step 5: A baby obviously has a real mouth and can smile, which contradicts the clue "never smiles." Step 6: Conclude that the best match for "has a mouth but never smiles" is a river.

Verification / Alternative check:
To verify, think about how you would describe these options in everyday language. You regularly hear about the "mouth of the Ganges" or the "mouth of the Nile" in geography lessons. You do not typically speak of the "mouth of a cave" in standard terminology, even if the idea appears occasionally in storytelling. A baby not only has a mouth but is known for smiling frequently, especially in family photos. This analysis confirms that the riddle specifically points to a river.

Why Other Options Are Wrong:
A cave or a volcano can have an opening, but their mouths are not standard phrases taught in school in the same way as "river mouth," and they do not form the basis of this well known riddle. A baby directly contradicts the riddle because babies can and do smile, and they have real mouths intended in the simplest sense of the word. As a result, these choices do not fit the tricky double meaning of "mouth" that makes the riddle work.

Common Pitfalls:
Many learners initially think of things like caves or animals and forget that geography uses the word "mouth" in a special way. Another common mistake is to overlook basic school terminology such as "source" and "mouth" of a river. To solve riddles like this more reliably, always consider whether the word in question might have a technical or metaphorical usage beyond its everyday meaning.

Final Answer:
The thing that has a mouth but never smiles is a river.