The tip of the tongue (apex) and the underside of the tongue (subapical region) are used to produce retroflex sounds.
In retroflex sounds, the tongue tip curls backward toward the alveolar ridge or hard palate without making firm contact.
These sounds are common in languages like Hindi, Tamil, and Mandarin Chinese, but they are not native to standard English.
Examples of retroflex sounds (in IPA): /ʈ, ɖ, ɳ, ʂ, ʐ, ɭ, ɻ/.
