In a manner of speaking. Deeper in the neck of the cervix, it is tighter there, that's what I meant. Unless you do extreme stretching which is difficult and painful. Check out Maya Simons at OnlyFans. She does the most extreme cervix penetrations you will ever see, if you have any interest there. Note: she does not post directly in that site because of the extreme nature of the content, but she does require you to have a membership. She will then email a link about once a month to you, where you can then view and/or download content. You will have to message her in OnlyFans to give her an email address to do that, and the subscription needs to be current. I will not repost any of her content here from that site, as I believe in supporting the model. However I have posted a bit here from stuff already found on the internet, awhile back, before I was a member of her site. Another note: It's best to use the Chrome browser, not Firefox, as I found that Firefox does not always work well with OnlyFans. I'm getting off-topic here, but you now have the info, if you wish to see the most extreme cervix content ever!
It's real. The inner sphincter prevents the marbles from going into the uterus. I'm not sure what the tube is, but I'm sure you can buy rubber or silicone versions of that thing these days.
Imagine its not marbles, but some mans castrated balls, that she cut off at surgical precision and then push them two inside her womb, deep into the end of fallopian tubes. One by her left ovary egg the other by her right egg. And those balls stay inside her womb by her tight to her ovary eggs for a week or two. Until her ovary eggs absorb all the semen out of those balls. And impregnate her.