There is some kind of animal in my room.

[Wicked Nick]

Damn Critters! I get those little bastards all the time!!

[Derf]

I think it was probably Howie Mandel. Those darn under-the-bed monsters just have too much fun scaring cats. But don't worry; they also have hearts of gold (so you might want to try ripping it out of his chest with your kung fu if he ever comes back).

[Zapranoth]

Yes, that was the little monster from the closet -- the episode was "Inside the Closet."  Ash posted a link to it on youtube.

Scared the p**s out of me when I first watched it.

[Scott]

Akiratubo, you had a close call. Is it safe now?

[Poogie]

It was probably a racoon or a possum.
Possums will growl loudly if they feel threatened.

Reminds me of the time I was in my old apartment sitting at my computer with the balcony door wide open.
Out of the corner of my eye I see this furry shape come through the door.
It was one of the biggest racoons I'd ever seen!
The thing just stared at me and then started to come in like he owned the place.

I yelled at it, "Get outta here!  Scat!" which didn't phase it.
I finally had to get up out of my chair and stomp my foot on the floor.
It casually walked back out.

You reminded me of the time (this should be a new topic) of when I went out to the garage to get the clothes out of the dryer and I heard a noise on the shelf by my right shoulder. I thought it was one of our cats, so I moved right up to it to see it better, and it was a raccoon, I let out a strange noise and jumped back. It just looked at me and started giving itself a bath.   

[Shadow]

Speaking of unwanted animal visitors, a few years back when I was single and living by myself, I was at home one night watching TV. I was on the couch with all the lights out except for the television. Out of the corner of my eye I see something run across the carpet from the direction of the front door. In that split second between the time my peripheral vision caught it and when I turned to look directly at it, my mind analyzed the fact that it was big enough to create a sizable shadow across the floor as well as make a sound as it scurried across the carpet, thus I concluded that a mouse had gotten into the house.

Imagine my utter horror when I turned to look right at it and realized it was a spider...one large enough to create a sizable shadow and make sound as it walked. To say that I freaked out big time is an understatement on par with calling Godzilla and inconvenient lizard.

[Torgo]

I knew some people who had the misfortune of a deer crashing through their living room window at their house/cabin and proceeding to freak out causing much strife and despair. 

[Dr. Whom]

As a test, I took one of my cats in my room and tossed it under my bed.  Something growled, not like a cat or a dog, and my poor cat hauled ass out of the room.

So, for all you know you may have a monster under your bed, and you send in a cat on a suicide mission! You heartless beast!