Thin, Detailed
A rice paddy that's like a thread is extremely thin, but also detailed.
Imagine a rice paddy in the form of an extremely thin, but also detailed piece of thread. The size and detailing means you'd maybe be able to get one line of rice in there? Seems very inefficient.
さい
ほそ, こま
None
This thin rice paddy is for your cyborg (さい). You only gave your cyborg a really thin strip of human stomach, so it only needs a thin line of rice to eat.
Picture the cyborg eating a really thin piece of rice. Now it's completely full! What a smart, thrifty cyborg!