The human heart contains four valves&colon; tricuspid valve, pulmonic valve, mitral valve and aortic valve. The glottis is closed so no pulmonic airstream is possible. Several Khoisan languages have limited numbers or distributions of pulmonic velar consonants. However, the series in Taa is characterized by pulmonic "ingressive" nasal airflow. Some pulmonic ingressive sounds do not have egressive counterparts. Nasal clicks involve a combination of lingual and pulmonic mechanisms. The words ('yes') and ('no') are sometimes pronounced with inhaled breath (pulmonic ingressive) in Norwegian. The lung pistons are used to initiate a pulmonic airstream (found in all human languages). However, pulmonic stops do have plosion in other environments. The normal mechanism is pulmonic egressive, that is, with air flowing outward from the lungs. The majority of sounds in most languages, such as vowels, are both pulmonic and egressive. There is no clear divide between pulmonic and glottalic sounds. Pulmonic egressive sounds are found in all spoken languages. Ingressive speech can be glottalic, velaric, or pulmonic. Pulmonic ingressive sounds are extremely rare outside paralinguistics.