The right side of frog rock has a death sieve below it. I am not saying that you can't make the move, it isn't that hard of a move to make but a fuck up has serious consequences and has been the site of numerous fatalities. So calling it an "eay" class II or whatever that means is not accurate.
You can scout it from the road on your drive up. Coming up the dirt road to railroad bridge from B.V. You will go through the tunnels and on your left hand side you will see elephant rock which is a large monolithic rock and a parking area, park there and head towards the river. It will take you pretty much right to it.
Depending on the flow, if you have to run the right line the issue is a bunch of fucker rocks that you have to maneuver around above the sieve, most people get into trouble popping swimmers on these rocks and the people swim into the undercut or the sieve. Or the other thing that happens is they try to avoid these rocks go far right and can't make the quick move back left and flip on the big undercut/sieve rock.
We went for years running down there without a single issue then all of a sudden people where having all kinds of trouble there.
But to be honest with you the narrows at this level is not that great, the numbers are still fun, pine creek rapid is a bit mellower, and browns is even a better ride currently.
Hope this helps