All four sides of triangular zongzi can use complete leaves without extra bending. If you make zongzi into a square, you need to fold the leaves and buckle them, so as to connect any side with other sides without leaking rice. The leaves are tough along the plant fiber direction, but easy to break in the vertical direction.
Tetrahedron is not very common in real life, and it is difficult to imagine its shape just by listening to its name. In fact, it has a more acceptable name-triangular pyramid.
All triangular pyramids have six edges, four angles and four faces, each face is a triangle, each triangular face is opposite to an angle, the bottom face is a regular triangle, and the other three faces are equal (must be isosceles triangles), which is called a regular triangular pyramid. If the bottom surface is completely equal to the other three surfaces, then these four surfaces must be regular triangles, so this is called a regular tetrahedron.
The origin of eating zongzi:
In 278 BC, on the fifth day of the fifth lunar month, the general of Qin took the lead in attacking Yinghou (Shouxian, Anhui), the capital of Chu.
When Qu Yuan learned the news, he was filled with grief and indignation. He wrote his masterpiece Huai Sha, and then he threw himself into the river with nostalgia and sorrow for his country.
Later generations, equally loyal and patriotic people, remembered the patriotic poet Qu Yuan. In order to prevent fish and shrimp in the water from eating his body, they threw glutinous rice, salted eggs, meat and other ingredients into the river.
With the passage and evolution of time, it has gradually become a custom to wrap these ingredients in zongzi to commemorate Qu Yuan during the Dragon Boat Festival. This is the origin of eating zongzi to commemorate Qu Yuan on Dragon Boat Festival.