* "shh" (an interjection)
* "psst" (an interjection)
* "brr" (an interjection)
* "mph" (an interjection)
* "tsk" (an interjection)
* "hmm" (an interjection)
* "ugh" (an interjection)
* "grrr" (an interjection)
These are usually considered interjections or onomatopoeia, representing sounds.