How do I make it so that the npc doesn't die automatically?

I madea bear npc, I was wondering if the two front legs are causing this problem, because I named them the arms, what should I name them, nothing? Because they may be causing the bear to die automatically.

Left arm and right arm

My Friend tried doin Zombies in his Place and wen he Added a Triangle Generated Terrain, the Zombies kept dying :/ Maybe it's something to do with terrain also?

Changing the Names of the NPC's Parts of the body can cause that, or they aren't welded together correctly. Both arms should be Left Arm and Right Arm, legs should be Left Leg and Right Leg, torso Torso, head Head, but as previously said it could be not welded together correctly. I hope this helped!