The hu indicates the habitual tense.
kunusa = to smell/sniff something
hunusa = smell(s)/sniff(s) something habitually
The hu also appears on the "you do not ..." form of verbs, the negative present for the 2nd person singular, but remember than in the negative present, verbs with a final "a" change this to "i"
Hunusi = You do not smell/sniff something