Hmmmmmmmmm....
She thought to herself.

Bzzzzzzzzzzzzzzzz....
The bee worried the flower.

Zzzzzzzzzzzzzzzzz....
Snored the man in the chair.

Ssssshhhhhhhhhhh....
The librarian shrieked.

Mmmmmmmmmm.....
Heard during a long kiss.

Ooooooooooooh.....
Surprised by unexpected gifts.

Uuuummmm..........
Unsure of the right words.

..............................
Silence also speaks volumes.