Firstly..... why have I never heard of this before? If it's real  then 'OOOOOWWWWWWWWWW'.
Secondly...... definitely not for the squeamish, it cannot be unseen, I may unclench again some time in March! Don't blame me.
Thirdly........ Common household glass objects aren't intended as toys, maybe it's better to  do a bit of online shopping for your  extremes than have to explain some nasty lacerations to  the nurses, doctors and observing medical student group in A&E. Look for the kitemark folks :shock:   
    
  
 
 :lol:
Really....perfect for disguising the blood.... so considerate of you two lol lol lol
:lol:
Really....perfect for disguising the blood.... so considerate of you two lol lol lol