Circular breathing is a technique used by players of some wind instruments to produce a continuous tone without interruption. This is accomplished by breathing in through the nose while simultaneously pushing air out through the mouth using air stored in the cheeks. (Wikipedia)

VERB

1. to laugh lightly in a nervous, affected, or silly manner (Google)
2. to laugh in a nervous or childlike way (Merriam-Webster)
3. to laugh with repeated short catches of the breath (Merriam-Webster)
4. to laugh gently or in a high-pitched voice; to laugh in a silly or giddy way (Wiktionary)

NOUN

1. a light, silly laugh  (Google)
2. a silly, spasmodic laugh; titter (Dictionary.com)
3. A high-pitched, silly laugh (Wiktionary)

Wikipedia

Sotto voce (/ˈsɒtoʊ ˈvoʊtʃeɪ/; Italian: [ˈsotto ˈvoːtʃe], literally “under voice”) means intentionally lowering the volume of one’s voice for emphasis. The speaker gives the impression of uttering involuntarily a truth which may surprise, shock, or offend. Galileo Galilei’s (probably apocryphal) utterance “Eppur si muove” (“Nonetheless, [the Earth] does move”), spoken after recanting his heliocentric theory, is an example of sotto voce utterance.

Mirriam-Webster Dictionary

under the breath :  in an undertone; also :  in a private manner – very softly —used as a direction in music

Cambridge Dictionary

said in a quietvoice so that only people near can hear:

Medical

Vocal fry occurs when the vocal (arytenoid) cartilages squeeze together very tightly.  This allows the vocal cords themselves to be loose and floppy.  When air passes between them, they can vibrate irregularly, popping and rattling. We used to believe that vocal fry suggested a voice problem.  However, after years of seeing young women with this pattern in their speaking voice, and seeing relatively normal looking vocal cords, I have begun to question this.  While undoubtedly this is not “normal” speech and will result in damage, it is increasingly accepted in music and speech in the teenage and 20-something set.  It does not always indicate a vocal cord problem exists; rather it is a usage problem.

Popular

The vocal fry register (also known as pulse register, laryngealisation, pulse phonation, creak, popcorning, glottal fry, glottal rattle, glottal scrape, or strohbass) is the lowest vocal register and is produced through a loose glottal closure which will permit air to bubble through slowly with a popping or rattling sound of a very low frequency. During this phonation, the arytenoid cartilages in the larynx are drawn together which causes the vocal folds to compress rather tightly and become relatively slack and compact.

Online

In speech, a low, scratchy sound that occupies the vocal range below modal voice (the most commonly used vocal register in speech and singing). Also known as vocal fry register, creaky voice, pulse register, laryngealization, and glottal fry. (See Examples and Observations, below.)