Normal Reactions = Horror worthy scenes

Right.  I just showered and shit about 10 minutes ago.  I feel great.  See, we had no water earlier so taking a bath wasn't a good option [unless you want to turn into a soap and shampoo monster].  Needless to say, I thought:  "Hey.  I wonder how long I could take not having a bath?"  Easily answered.  The moment I uttered that question, I immediately felt the need to take a bath.  Genius.  But hey, at least give me credit.  I took a bath around 5:08 pm.  What does that say, huh?

"You are a disgusting excuse for a woman."
*Insert Okay-meme face here*

Annnnnywho, I was brushing my teeth.  Naturally, my head was bent down over the sink.  Suddenly...the unthinkable happens.  I feel a drop of something fall on my head.  I stopped.  I felt myself shudder.  I squeezed my eyes shut and ignored it.  I continued brushing my teeth.  Then another drop of whatever fell on my head.  Again.  My eyes widened...slowly, I looked up...and saw...

A bunch of wet underwear, hanging above the sink to dry.

*Ba dum tsssss..*

Can you see how a normal reaction to a mundane thing can turn into a really great inspiration for horror movie scenes?  I guess there's not so much magic to it.  Basically, these scenes tap into the minds of a normal human being's perception on how he/she'd react to a certain event.  This is not the only example I can give you.  Normal mundane thing = Horror movie scene in 3...2...1...

She went into the second floor bathroom.  She heard someone shuffling.  She called out: "Is anyone there?"  Silence.  She saw the door of the last stall open, its door creaking.  She heard a sob.  She gulped.  She walked towards the stall and blinked.  She was tempted to run away, yet tempted to look at it at the same time.  She followed the latter instinct.  Bracing herself for whatever was in there, she opened the door.  She screamed as she saw...

Her office mate Tina taking a huge dump.

See what I mean?  Change some elements, and you've got yourself a horror worthy movie scene.
It's not everyday that one sees something so horrifying...but with a wee-bit of imagination, I bet you can come up with something terrifying.