I did that the first time when I was 12 years old. It took 40 years for me to do it again. I seem to do it when I am trying to hurry and get finished-I just run my finger right up in there! The first time when my Mom pulled the needle out, everytime my heart would beat, blood would spurt out-not a pleasant situation to be in for sure! Luckily, both times, I had just had a tentanus booster.