Fake poop. My nephew got fake poop a few years back and he's managed to repeatedly make me, both of my sisters, my niece, my mom and even my cat think that it's actually a piece of crap. The boy's a natural when it comes to biding your time. He waits until we've all completely forgotten that he even has it and then he puts it in a really bad place and watches us get disgusted. Although it was pretty funny when he brought it over and placed it next to my cat, because my cat leaned backward and was like, "Whoa, whoa, whoa, Jesus! Get that away from me you crap freak!"
But, yeah, fake poop. Guaranteed to provide hours and hours of fun. Don't hesitate, buy some today!