The beads may be made of teflon, {HEAD ~ polystyrene}, polyethylene, or any other suitable particulate material that absorbs {TAIL ~ vibration energy} when vibrated to cause rubbing between the beads 
The beads may be made of teflon , { HEAD ~ polystyrene } , polyethylene , or any other suitable particulate material that absorbs { TAIL ~ vibration energy } when vibrated to cause rubbing between the beads
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