Complex sentence: Cats that were caught drinking lamp oil were also considered to be "bake-neko" s. Cat monsters may have regularly been caught drinking lamp oil due to the fact that old fashion lamp oil was made from fish.
Split into simpler sentences: Cats that were caught drinking lamp oil were also considered to be "bake-neko". Cats may have regularly been caught drinking lamp oil due to the fact that old fashion lamp oil was made from fish.