Cheek pit - Kyouka

...The tongue also senses air vibrations, currents, and temperature differences. The upper lip plate of pythons and the pits (also called pits or pit organs) located in front of and below the eyes of Crotalinae pit vipers are temperature-sensitive organs. The pits of pit vipers in particular are separated by a thin membrane and are sensitive to subtle temperature differences between the two chambers, inside and outside. The pair of pits on the left and right sides captures infrared rays emitted from the body surface of mammals and birds in three dimensions, allowing them to accurately drive their venomous fangs into prey even in the dark and to attack dangerous enemies, including humans.

*Some of the terminology that mentions "cheek pit" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…舌はまた空気の振動や流れ，温度差などをも感じとる。　ニシキヘビ類の上唇板とマムシ類Crotalinaeの眼の前下方にあるピットpit(頰窩（きようか），孔器ともいう)は温度に敏感な器官で，とくにマムシ類のピットは薄い膜で仕切られ，内外2室の微妙な温度差を敏感に読み取る。左右1対のピットは哺乳類や鳥類の体表から発せられる赤外線を立体的にとらえ，暗闇でも正確に獲物に毒牙を打ちこみ，また人を含む危険な敵を攻撃することができる。…

※「頰窩」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報