its mouth to mouth when the oral cavity is not obstructed or there isn't blood for eg, but when the oral cavity is obstructed then is mouth to nose

They are the means to get air (oxygen) into the lungs.

The mouth part of a river is called a delta. It is the large silty area at the mouth of a river at which the river spills into different slow flowing channels.

The mouth of the river is the Fremantle ocean which is in South Australia.

The word "mouth" in the Chinese language is 口 (kǒu).