When Celia was growing up, her father had taken in a stray kitten, an avid hunter who – by the time Celia had left for college – still had not gotten over a formative, stray-life trauma that compelled it to mewl between mouthfuls of food.
-- Myla Goldberg, The False Friend
They have mouths that twitch, and eyes that stare, and they babble and they mewl and they whimper.
-- Neil Gaiman, Smoke and Mirrors
Mewl is an imitative word that mimics the sound of a whimper.