The German interjection "hm" is used like "um" but can mean more:

"Hm" = I'm not convinced.

"Hm, hm" = Well, well.

"Hmm" = Let me think.

"Hmmm!" = That's yummy!

"Hmmmm..." = Good point, never thought of that!

"Hm hm hm hm hm hm hm hm!" = Please take that gag out of my mouth!

Enjoy our language!