Not sure about the shapes, but got this tip directly from a watermelon farmer in Taiwan which is known for very sweet watermelons.
The heavier it is, the more sugar content there is.
To confirm this is to uniformly pat the watermelon to listen for a deeper sound(compared to the other watermelons nearby… Sound travels through sugar slower so the sound is deeper.
Not sure about the shapes, but got this tip directly from a watermelon farmer in Taiwan which is known for very sweet watermelons.
The heavier it is, the more sugar content there is.
To confirm this is to uniformly pat the watermelon to listen for a deeper sound(compared to the other watermelons nearby… Sound travels through sugar slower so the sound is deeper.