口角

1. Origins, structure, and basic meaning

• Structure: 口角(こうかく) is either corner of the mouth where the upper and lower lips meet.
• Basic usage: It is used for the corners rising with happiness or their movement viewed in a mirror.

2. Common pitfalls and similar expressions

• The on-reading of 角
  • Unlike 角(かど), meaning a corner, 角 is read かく in this word. The preceding 口 is read こう, forming the compound.