What happens under the muggins rule when a player misses points in cribbage?

In the game of cribbage, the "muggins" rule is an optional provision where, if a player fails to claim their full score during their turn, their opponent may call out "Muggins" and claim those overlooked points for themselves.1

Because cribbage requires players to track their own scores, this rule serves as a penalty for failing to record earned points promptly. It is important to note that this is not a universal rule and is only applied in games where the participants have specifically agreed to include it.21