The mouth being open. Only use when sufficiently open to (theoretically) see inside.
If the mouth is only slightly parted use [[parted lips]].

The opposite of this is [[closed mouth]].

h4. See also

* [[ahegao]]
* [[cum in mouth]]
* [[mouth pull]]
* [[parted lips]]
* [[tongue]]
* [[uvula]]
* [[white mouth]]
* [[:o]]
開口 開いた口