Similar English Phoneme: Like "ts" in "cats" and "students".
The pronunciation of an initial consonant is very short.
Actually, what you hear is a syllable pronounced as a whole ,as shown below:
z: un-aspirated, the airflow is weak when pronouncing z.
c: aspirated, the airflow is relatively stronger when pronouncing c.
Put your hand in front of your mouth to feel the airflow.