1) Acts contentedly 2) Cat sounds 3) Contented cat sounds 4) Contented sounds 5) Copies a happy cat 6) Engine hums 7) Expresses pleasure 8) Feline rumbles 9) Feline utterances 10) Good engine sounds 11) Hums like an engine 12) Manx thanks 13) Motor sounds 14) Murmurs contentedly 15) Runs great 16) Runs like a top 1) Hums