Poison Won't Damage The Target If We Didn't Stop Hitting The Target?

I tried hitting deltas citizens serveral times without delay, and the poison damage didn't appear.(no particle effect)
But when I try to stop hitting them or give a few milliseconds attack delay, the poison damage appear.(with particle effect)
It may be because the poison effect keep getting refreshed that it didn't even start damaging

 

Does your weapon say something like: Poison 2/1? It could just be the poison doesn't last very long on your weapon.

 

no, it say 15/3, 3 seconds was long enough. When I give a delay to my attacks it shows my neutral weapon damage and the poison damage separated and a particle effect around the villagers, meanwhile when I attack the villagers without delay theres no particle effect