Here's why:
* Gerund: "Laughing" is a gerund, which is a verb form ending in "-ing" that acts as a noun.
* Subject: The subject of a sentence is the person or thing that performs the action of the verb. In this sentence, the action is "is good," and the thing performing that action is "Laughing."
Therefore, the gerund phrase "Laughing" acts as the noun that is the subject of the sentence.