On Pesach, anything that is rauy l’achilas kelev (can be eaten by a dog) is considered chametz. The Shulchan Aruch (OC 442: 9) writes that once it becomes unfit, one may own it over Pesach. The Mishna Berura (442:43) qualifies this ruling: while one may own it, one is still forbidden to eat this inedible ‘food’ miderabanan (See Rosh, Pesachim 2:1).
How this rule applies to modern substances, however, doesn't seem without question. For instance, should one throw out Play-doh and similar products before Pesach? (For another decidedly modern application, see here.)
From the Play-doh website:
...it is primarily a mixture of water, salt and flour... It DOES contain wheat. Play-Doh compound is not a food item and is not intended to be eaten.
Play-Doh compound is non-toxic, non-irritating & non-allergenic except as noted: Children who are allergic to wheat gluten may have an allergic reaction to this product. Also, due to the high salt content in Play-Doh compound, the product can be harmful to pets if ingested.
(See also: https://www.google.com/patents/US6713624 )
Assuming it is basically flour, water, salt, and coloring, is it considered chametz or taarovet-chametz and is it considered ra'uy l'achilat kelev. More specifically, does rauy l'achilat kelev mean that something would typically be used as dog food, or that it is non-toxic and has nutritive value and a dog would eat it? (I've so far found random sites on the internet that claim both ways, but was curious if anyone's come across a more definitive ruling with sources and/or explanations both for the general rule and the particular example of Play-doh.)