The black liquid snake attached to the long sword was actually a part of the previously mentioned black spike, and was entirely brought into existence by a malicious curse.
Once contaminated, one would suffer from endless torment of the curse, eventually leading to a tragic death with no spiritual release.
If Song Jian had not acquired the Golden Demonslaying Sword, trying to dispel the curse using solely the Crimson Fire Heart Ape Sword would have been impossible. The consequence could have been substantial damage to the Ape Sword, requiring a long time for restoration.
The Golden Demonslaying Sword possesses properties to destroy evil which counteracts such attacks. Coupled with Song Jian's execution of the technique of the Sacred Parry, the majority of the curse was deflected. This made the curse easily dispelled.
