Answer:
The word "huh" (surprise or confusion) is included in many lists of onomatopoeia, while the words uh and er (hesitation) are not. All are created by a mostly unshaped exhalation of air.
*Both uh and huh are similar to the "whuh" (blowing sound), which may have influenced the English word "what" (Old English hwaet). Both hwa and the Latin quo may have developed from a common proto-language form kwo.