Idk I sort of just did this...

(Break of character - in case you couldn't tell, this is a shitpost)

To go through an existing piece of crochet, consider the "working" fabric, and the "stale" fabric (I.e. the one you are currently making, and the one you have already made).  Then to put the working fabric through the stale fabric, 

1. Line the fabrics up in 3d to where they will be in the finished piece. 

2. Think about the next hypothetical stitch in the working fabric and where it will be. 

3. If this stitch will intersect the stale fabric, consider where in the new stitch this will happen. 

4. Do the new stitch as normal, except put the hook through the stale stitch so it gets stuck in the place you thought about from step 3. This may require trial and error. 

5. Continue as normal. To get stitches on the other side of the stale piece, pull the *entire ball of yarn* through the stale piece by the tail.  
If someone accidentally did this process I would be stunned.