Learn Turkish: Sahipsiz yavrucağız giderek daha mahzun görünüyordu. - The poor stray little one was looking gradually sadder.

The suffix -cağız (or -ceğiz) is a diminutive that adds a strong sense of compassion, pity, or endearment. While yavru just means "young animal" or "little one," adding -cağız gives the feeling of "the poor little thing." It highlights the speaker's sympathy for the ownerless animal.

I know gitmek means "to go." Why does giderek mean "gradually" here?

The suffix -erek normally means "by doing" an action. While giderek literally translates to "by going," it has evolved into a set adverb in Turkish meaning "gradually," "increasingly," or "step by step." When paired with daha (more), the phrase giderek daha mahzun means "increasingly sadder" or "sadder and sadder."

Why is the verb görünüyordu instead of görüyordu?

Görüyordu comes from the base verb görmek (to see) and means "was seeing." Because we want to say the animal "was looking" or "appearing" sad, we need the verb görünmek. Adding the reflexive suffix -ün to gör- changes the meaning to "to appear" or "to look." The suffixes -üyor and -du then make it past continuous.

Could I just use the word üzgün (sad) instead of mahzun?