Emma's scenes in the dungeon (especially Squirtathon and orgasm denial) seems to have some lagging/slow issue (and even, the screen goes to the choice of activity in MC room for one frame before it comes back to the dungeon scen). (On pc)
I was going to accept my "outdated hardware" explanation since my pc is from 2012 but i had still some trouble with it because:
1) no other scene has really this trouble in this game
2) i can still play some more demanding games.
3) i have played many other games with the same engine and no such issue in those.
Now that another poster has the same issue, i'm not so sure at all. I'd advise Runey42 to check if anything is different in those scenes.
Yeah, it's the frame rate. These aren't frames like FPS frames, these are dozens of individual image frames at 1920x1080, being flashed on your screen very fast (60 images in a second) so if your computer can't store all those images, it will lag.
Most other animations are in 24 frames, so it's much less data to store, and isn't being flashed as fast on screen.