Oddly that sequence was one of the few true special effects sequences. The cat had honey smeared on its coat and the tame rats obligingly licked it off. The cat lived happily ever after.
Other gruesome sequences used actual body parts sourced from a morgue as they didn't have the budget to make convincing splatter effects and the director really wanted to make a serious film highlighting the Japanese war atrocities he felt the world was forgetting. After it became an international hit, especially among the VHS grue merchants in the US, the Chinese production company started churning out more and more even cheaper knock-offs with more and more crappy SFX, but none of them had the serious intentions of the first one.