"My mouth is open."
Some two syllabled nouns, whose second vowel is ı/i/u/ü, drop these vowels when used in accusative, dative, genitive and possessive.
Ağız → ağzım, ağzı, ağza, ağzın
A lot of body parts are in this category: om(u)z (shoulder), kar(ı)n (stomach), al(ı)n (forehead), bur(u)n (nose)
But also some random words: şeh(i)r (city), res(i)m (picture), vak(i)t (time), nak(i)t (cash), uf(u)k (horizon)