Meow and Cat Eyes keys
Meow and Cat Eyes · mechanic, keys · Catgirl & Catboy Mod
The mod has two keys. Both can be changed in the controls screen: Meow is in the Multiplayer category, Cat Eyes (night vision) is in Gameplay.
Meow
Z makes your character meow. It needs no items. Everyone nearby hears it, and three notes fly up above your head. In the Full Neko set four hearts fly up as well.
Up to six of the nearest cats and ocelots within 12 blocks answer one after another: each turns to you and makes its own sound within a second and a half.

The key works once every 1.5 seconds. It does nothing while a screen is open (inventory, chat) or in spectator mode.
The first meow grants the advancement First Meow. A meow with five or more cats or ocelots within 8 blocks grants Herding Cats.
The default is Z and not M because M opens the map in Xaero's World Map.
Cat Eyes
N gives Night Vision for 10 seconds. It works only in the complete Full Neko set: ears, tail, collar and paws. Without the set the game reminds you which pieces it needs.
The cooldown is 30 seconds and starts when you press the key. So the next use is possible 20 seconds after the effect runs out. Press earlier and the seconds left show up above the hotbar. The cooldown isn't saved: it is gone after you leave the world or the server restarts.
Sounds
The meow is the vanilla cat meow at a higher pitch. The mod has no sound files of its own.