A general rule of English pronunciation states that the 's' in plural nouns is to be pronounced as /z/ if it is preceded by a 'voiced consonant' such as /n/ or /g/, and as /s/ if it is preceded by a 'voiceless consonant' such as /t/ or /p/.
Therefore, "pens" is pronounced as /penz/ and "cats" is pronounced as /cats/.
Now my question is, do native speakers of English always follow this rule? Secondly, and this is what I really need to understand, does this rule apply also to the 's' in the verbs of 'third person singular subjects'?
–Prasad (Bangalore, India)