In a world where people have elastic arms that can stretch infinitely without any harm, Yara and Takashi stand on opposite sides of a large, opaque wall that reaches up to the sky and penetrates deep into the earth, with no way around it. Yara and Takashi both stretch an arm over the wall to high-five each other. Considering the wall is completely opaque, how does Yara know when Takashi's hand is high enough for a high-five? Provide a very short response.
Yara knows when Takashi's hand is high enough for a high-five by feeling the contact of Takashi's hand with her own. The sense of touch provides immediate feedback when their hands meet at a certain height, indicating the proper moment to perform the high-five, despite the visual obstacle created by the opaque wall.