It's think, you, koko, ken.

Explanation:

1. The eye is at the top of the heart, so the answer is "think".

2. The answer is "you" because the person stays on the side of the word "you".

3. The word "d" can be used as the word "d" and the word "mouth", which is "can".

4. The word "stop" can be used as the character for "stop" and "moon", and the answer is "ken".

Expanded:

Crossword puzzles, like any other form of art, are most memorable and attractive because of the way they are written. The most attractive thing that attracts people's attention is its external manifestation - the riddle. The face of the riddle is a concentrated expression of the essence of the art of crossword puzzles.

It usually consists of short and concise words, phrases, sentences or ballads and poems with the ability of image expression. The language of the riddle has very special requirements. First of all, it should be simple and clear, vivid image, easy to understand.

The riddle of a word puzzle must be vividly expressed with the help of the image of the thing, which is the main feature of the Chinese character at the bottom of the riddle. Piling up long, obscure and boring conceptual terms will not be welcomed. Secondly, the main content of the riddle, such as the strokes and shapes of the Chinese characters or the meaning of the Chinese characters and other typical features, should be summarized in a highly concentrated way, so as to provide a true and reliable basis for people to find and reveal the answer to the riddle.