How do I add procedural muscular spasms to a Humanoid Rig? (electrocute, seizure)

Hi there!

I'm trying to get what I thought to be a simple position/rotation noise to the bones of a Humanoid Rig. I need it to simulate muscular spasms induced by a venom on a character, and the attempt of the character to resist. I would also like to recycle the effect to simulate the electrocution of a character. I'm pretty sure it can be done without third party plugins, so I'd prefer a solution efficient enough to run on mobile (single character)

I tried to write a StateMachineBehaviour, but, well, my hope that only animating the IK targets would result in something decent failed miserably.

Is there a way to use the muscles like those in the avatar? I have no idea on how to iterate each bone/muscle to apply some jitter.

[would be nice if the body stayed in place, I don't want the character to jump out of the camera during a cutscene :P ]

Here's what I wrote. Please note that I can successfully trigger it using Mecanim, but the effect itself is pretty lame :P

     using System.Collections;
     using System.Collections.Generic;
     using UnityEngine;
     
     public class AnimStateSeizure : StateMachineBehaviour
     {
         public float initialSeizureAmount;
     
         public float targetSeizureAmount;
     
         public float interpolationSpeed;
     
         public float currentSeizureAmount;
         
         
         // OnStateEnter is called when a transition starts and the state machine starts to evaluate this state
         override public void OnStateEnter(Animator animator, AnimatorStateInfo stateInfo, int layerIndex)
         {
             currentSeizureAmount = initialSeizureAmount;
         }
     
         // OnStateUpdate is called on each Update frame between OnStateEnter and OnStateExit callbacks
         override public void OnStateUpdate(Animator animator, AnimatorStateInfo stateInfo, int layerIndex)
         {
             currentSeizureAmount =
                 Mathf.Lerp(currentSeizureAmount, targetSeizureAmount, interpolationSpeed * Time.deltaTime);
         }
     
         // OnStateIK is called right after Animator.OnAnimatorIK()
         override public void OnStateIK(Animator animator, AnimatorStateInfo stateInfo, int layerIndex)
         {
             // Implement code that sets up animation IK (inverse kinematics)
             Spasm(animator, AvatarIKGoal.LeftFoot);
             Spasm(animator, AvatarIKGoal.RightFoot);
             Spasm(animator, AvatarIKGoal.LeftHand);
             Spasm(animator, AvatarIKGoal.RightHand);
         }
     
         private void Spasm(Animator animator, AvatarIKGoal ikGoal)
         {
             animator.SetIKPosition(ikGoal, animator.GetIKPosition(ikGoal) + Random.insideUnitSphere * currentSeizureAmount);
             animator.SetIKPositionWeight(ikGoal, 1f);
             animator.SetIKRotation(ikGoal, Quaternion.FromToRotation(animator.GetIKRotation(ikGoal).eulerAngles, Random.insideUnitSphere * currentSeizureAmount));
             animator.SetIKRotationWeight(ikGoal, 1f);
         }
     }