Learn Spanish (Latin America): Vi a la jirafa al lado del elefante y la escuché masticar. - I saw the giraffe next to the elephant and I heard her chewing.

While it is called the personal a, it is also commonly used for specific animals, especially pets or animals you are observing closely as individuals (like at a zoo). Since the speaker is pointing out a specific giraffe, a la jirafa is the correct choice here.

Why does the sentence use the infinitive masticar instead of the gerund masticando for "chewing"?

With verbs of the senses like escuchar and ver, Spanish heavily prefers using the infinitive rather than the gerund. While la escuché masticando is grammatically okay, la escuché masticar is much more natural and common, even though we translate it as "I heard her chewing" in English.

Why does la go before escuché? Can I attach it to the end of masticar?

No, you cannot attach it to masticar in this structure. When using a perception verb plus an infinitive, the object pronoun (la, representing the giraffe) is tied to the conjugated verb (escuché). Therefore, it must go immediately before it: la escuché masticar.

Just to be sure, why is it del elefante?