Suppress yawning
التَّثَاؤُبُ مِنَ الشَّيْطَانِ، فَإِذَا تَثَاءَبَ أَحَدُكُمْ فَلْيَرُدَّهُ مَا اسْتَطَاعَ
At-tatha'ubu mina-sh-shaytan, fa-idha tatha'aba ahadukum fa-l-yarudd-hu ma-stata'.
"Yawning is from Satan. When one of you yawns, let him suppress it as best he can."
Narrated by Abu Hurayrah. Sahih al-Bukhari 6223
A short reflection
A tiny instruction. Cover the mouth, hold the sound. The shaytan smiles at slackness; cover the moment.