One of the quintessential thriller movies is Alfred Hitchcock's Psycho. Who can forget the shower scene in that movie? For $19.99 plus shipping you can order one of these to frighten your guests from Think Geek.
Or you can do what I did, and buy yourself a dollar store shower curtain,
pour out some craft paint,
and get a little messy. You need a few hand prints.
And some random blood splatter, after all knives create blood splatter. We know this from too many Law & Orders, Bones, and CSI shows.
And just for good measure that last grasp falling hand smear.
After squishing the paint between my hands, I realized that I wouldn't be able to take any pics, so I hollered for WD to come take a pic of my hands before I washed them off.