The holes in honeycombs start as circular tubes staggered with one another. The heat formed by the activity of the bees then softens the wax, which connects the gaps between the holes. Finally, the wax hardens into the the most energy efficient shape, the hexagon. – WTF Fun Facts
wax
WTF Fun Fact – Da Vinci’s Oxen Heart Valve
Leonardo Da Vinci once created a replica of a heart valve by pouring hot wax into an oxen’s heart, making a mold of thin glass from the cast, and then pumping water mixed with seeds through it. He identified vortices which help close the heart valve after each beat. – WTF Fun Facts
Source: https://www.rct.uk/collection/919082/the-aortic-valve