Achilles' Heel

The video begins with Moon expressing difficulty in understanding math homework. The teacher reassures Moon and explains the concept of an 'Achilles' heel' using the Greek legend of Achilles. The discussion shifts to a humorous note as Moon jokes about needing magical water to improve math skills, and the teacher responds with laughter.

In what way has the usage of 'Achilles' heel' changed from the 19th century to now?

What humorous suggestion does the character make about improving math skills?