YUP, poop; someone will get a piece out that hard (or they hid it till it's hard)
Then the fun begins. Thank god it's not all the time, but every once in a while we hear something hard making a sound on the floor that's not familiar and guess what it is.
By the way shoes/ sneakers are far game, the older the better. They are great fun too nose dive in. They are also great if one of the kids gets mad, believe me it's not fun too slip in to a shoe that someone used as a urinal.
I wear deck shoes all year long and the older ones I use as slippers so there is always a supply of shoes to play in. I don't know why but they will also play in my wifes shoes, buy I get the presants in mine.