[D&D] Rats are menace

First mission for LuvMina. There is one mage's guild apprentise who doesn't go the way guild wants. And now he's disappeared. And who goes to investigate? Character of course. Character takes his NPC friend halfling thief Francis with him and they go to sewers where the map Luv gained shows this evil apprentice's lair is.

First fighting encounter! Rats, I thought, as it is a sewer. I checked that rats are 1/4 CR so there will be... um, 10 of them. Sounds good. They do 1D3-4 damage (I had no idea what that means... are damage dice exploding? Whether they are or not I have already decided so. But they were rats guarding the lair so I decided if they hit they do 1 HP damage).

What did I learn. I have always laughed at computer games (Morrowind, I am watching you) where you have to save at the beginning of the game before entering the cellar with rat problem. Rats do kill characters in computer games, and that is silly imo. So I thought, it cannot be the case in roleplaying games. How wrong I was.

Rat's didn't kill the characters. Halfling thief level 2 dropped from 9 HP to 4 and LuvMina had 2 points of damage total before she used Mage Armor spell. After that, rats didn't hit her anymore. Fight was furious. LuvMina has -2 to melee attacks so she didn't hit with her spear. I whispered her, that her character is a spell caster not a fighter, and response was that she won't waste her spells on some rats (I thought those will be character's last words).

But they managed to kill all 10 rats. Wounded, but did it. Luckily halfling has 4 healing potions worth of D8 HP (emergency kit of DM, as I am beginner in Dungeons & Dragons and not sure how hard some opponents are, those can fix the aftermath) and they both used them.
Rat guardians killed, reinforced door waiting to be lockpicked.

Next time some monster (gotta look MM) what is guarding bad apperentice's lair. Mushrooms (check my previous post) and turning quest back.

Those rats were worth of 375 experience points for first level sorceress LuvMina. Way to go. Only few exp to level up.