The "cliffside lake" scene can be unlocked by wearing the slimy black thong in the forest... and travelling to the East / Right, past the green slimes and trying to escape.
I believe the "pulsating strip of slimy rubber" scene is unlocked by losing the combat tutorial right at the beginning of the game!
Don't worry, you don't need to play through the entire game again. Just unlock these scenes on another file and they'll appear in your gallery at the end of the game!