"The boy doesn't wear socks."
Translation:הילד לא גורב גרביים.
In nikud-less writing, the i vowel is usually written (I won't go into the rules of when exactly, even most native Israelis don't know them). This is one of those cases. So the first י is the consonant y, and the second is the vowel i.
Therefore, in nikud-less writing, גרבים would be garvim (no such word), while גרביים = garbayim.
This is also needed in practice to remove ambiguity in many words. For example:
- Thousands: אלפים (alafim)
- Two thousand: אלפיים (alpayim)