The Mouth and The Lip
Scholars have said that if one sees their mouth hanging open or sealed shut, it may indicate disbelief (kufr). The lip is interpreted as a man's friend, helper, and support, with the lower lip having a stronger interpretation than the upper. The lips may also represent relatives or a close friend.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam