According to this classic riddle, what can you catch but never throw?

Introduction / Context:
This is a very common riddle used in English language classrooms and basic reasoning tests. It asks, "What can you catch but not throw?" On the surface, the word "catch" suggests physical catching, as in catching a ball. The trick is that "catch" in English also means to become infected with an illness, such as catching a cold. You can catch a cold from someone else, but you cannot literally throw a cold like you would throw an object. This double meaning of the verb "catch" is the heart of the puzzle.

Given Data / Assumptions:

• The thing can be "caught".
• The same thing cannot be "thrown".
• We must interpret "catch" in more than one possible sense.
• The correct answer should be a familiar concept from daily life.

Concept / Approach:
The word "catch" is used both in sports and in medical or everyday health contexts. You catch a ball with your hands, but you catch a cold when a virus infects you. Only the medical meaning fits the second requirement that you cannot throw it. An illness may be transmitted, but not in the physical tossing motion that the word "throw" implies. Among common illnesses, "a cold" is the standard answer used in many traditional riddle collections, and it appears in the option list as well.

Step-by-Step Solution:
Step 1: Identify that the riddle is playing with different meanings of the verb "catch". Step 2: Recall phrases where "catch" refers to illness, such as "catch a cold" or "catch the flu". Step 3: Check whether it makes sense to talk about "throwing" such things; clearly, you cannot throw a cold like a ball. Step 4: Compare this with physical objects like balls or fish, which you can both catch and throw. Step 5: Conclude that "A cold" is the only answer that you can catch but not throw.

Verification / Alternative check:
Consider each option carefully. You can catch a train or a bus in the sense of boarding them before they leave, but you could also argue that you can "throw away" a bus or train ticket, so the contrast is not as strong or standard. More importantly, the phrase "catch a cold" is a fixed and widely known combination in English, often used when teaching this exact riddle. You can certainly catch and throw a ball, which breaks the condition that throwing is impossible. A fish can be caught and then thrown back into the water. Only a cold behaves purely as an illness that can be caught but not thrown in any literal sense.

Why Other Options Are Wrong:
A train: You can "catch a train" in a figurative way, but you can also throw things associated with it, and the phrase is less iconic for riddles.
A bus: Similar to a train; the phrase exists, but it is not unique or central in traditional versions of this riddle.
A ball: Designed to be caught and thrown, so it fails the second requirement.
A fish: Can be caught and physically thrown back, so both actions are possible, not just catching.

Common Pitfalls:
One common error is to think only about the physical meaning of "catch", leading to answers involving sports or hunting. Another is to overlook set phrases in English, such as "catch a cold", which are key to understanding many word based puzzles. To avoid such mistakes, always pause and ask whether a word in a riddle might have multiple common meanings. Recognising idioms and fixed expressions is a powerful tool for solving language based reasoning questions quickly and accurately.

Final Answer:
The thing you can catch but never throw is a cold.