Left: mouth 口, right: investigate 察 (When there is a cover 宀 over the sacrificial 祭 item on the alter 示, it is to be investigated.) [祭 = The body 月/肉 is put by hand on the altar 示 as sacrifice]
Mnemonic
The mouth must be investigated if it makes cracking sounds.
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!