Rats World. A little world where rats wander and play.... what secrets does it hide?

This is an exploration puzzle game with somewhat obtuse mechanics and lots of hidden passages. It is a Sekret Santa gift for fotocopiadora. I didn't make it entirely by myself; I had some help with the audio from my friend Hubol (hubolhubolhubol.com).

Controls:
Arrow Keys or WASD: Move
Enter or Space: Action

Credits:
Graphics, Design, and Programming: Sylvie
Music and Sound: Hubol

If you get stuck, here are some general hints. Use ROT13 (rot13.com) to decode them.
- Gb svtug lbh jvyy arrq Urnyguf. Tnva vg ol rngvat guvatf bss gur tebhaq.
- Tnva Fgeratguf ol svtugvat engf naq fpbecvbaf. Fgeratguf yrg lbh chfu pregnva oybpxf.
- Tnva Jvfqbzf ol ernqvat obbxf. Jvfqbzf yrg lbh cnff fcrpvsvp bofgnpyrf.
- Tnva Punevfznf ol gnyxvat gb punenpgref. Fbzr punenpgref jvyy gryy lbh frpergf vs lbhe Punevfznf vf uvtu.
- Tnva Yhpxf ol svaqvat gernfherf. Lbh arire xabj jura vg jvyy uryc lbh.
- Jura lbh vapernfr Fgeratguf ol bar yriry, gel erivfvgvat byq nernf gb svaq arj oybpxf gb chfu.
- Jura lbh vapernfr Punevfznf ol bar yriry, gel gnyxvat gb punenpgref ntnva gb frr vs gurl gryy lbh arj vasb.
- Gurer ner frireny xvaqf bs frperg cnffntrf. Nf jryy nf snxr naq chfunoyr jnyyf, lbh pna svaq vaivfvoyr fgnvef!