Another thing that is a big factor in this is how turned on your girl is. The more turned on you are, the more the vagina legnthens and the cervix moves outta the way to make room for the penis- if your girl isn't totally turned on before you start having sex, there's a bigger chance you'll hit something!
It HURTS when you hit the cervix, no doubt about it. That's an organ that really isn't supposed to move that much- it can really kill the mood for us because it goes from feeling really good to feeling really OUCH!
Oh, and if you're new to sex- check out
The Guide to Getting it ON! by Paul Johannes. Best sex book EVER- I've recommended it to dozens of people and in tons of threads on TFP and haven't ever had anyone say they didn't like it or not learn something!
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Sage knows our mythic history, King Arthur's and Sir Caradoc's
She answers hard acrostics, has a pretty taste for paradox
She quotes in elegiacs all the crimes of Heliogabalus
In conics she can floor peculiarities parabolous
-C'hi