When you can’t play without passing 31, you say go. Your opponent plays any cards that fit, then whoever laid the last card scores 1 and the count resets.
During pegging, the running count can never pass 31. When none of your cards fit, you say “go” and pass. Your opponent then plays on alone, laying as many cards as will fit under 31.
When neither player can play, the last player who laid a card scores 1 point for the go — not the player who said go. The count resets to zero and the player who didn’t play last leads the next count.
If the last card brings the count to exactly 31, that player scores 2 for the 31 instead of 1 for the go. See do you score a go and 31 together?
The last card of all in the pegging round works the same way: whoever plays it scores 1 for last card (or 2 if it makes exactly 31).