What's a cow's favorite holiday?

The joke “What’s a cow’s favorite holiday? Moo Year’s Eve!” is a playful pun involving a play on words between “Moo,” a sound typically associated with cows, and “New Year’s Eve,” a widely celebrated holiday. The humor arises from substituting the word “New” in “New Year’s Eve” with “Moo,” thus creating a whimsical holiday name that sounds like it would be favored by cows. This kind of joke is common in light, family-friendly humor, where the amusement comes from altering a familiar term or phrase in a way that involves an element related to the subject of the joke—in this case, a cow.