Urinals are the only bathroom appliances that are regularly filled with cake. Well, technically, those cakes are actually “urinal deodorizer blocks,” and they do not look delicious. But why do urinals need the products, when toilets don't?
As the name indicates, urinal cakes are designed to offset the persistent scent of pee that otherwise permeates public restrooms (which have enough odor problems). Urinals tend to collect a lot of pee that doesn't always wash down the drain—and that residual urine can smell.
Thanks to the curious folks at SciShow, we now have a scientific breakdown of what exactly happens when urine sits around and why it becomes smelly. Urinal cakes—initially made of the same chemical in mothballs and now typically made up of a chemical named paradichlorobenzene—are designed to overpower and soak up the smells produced by all that urine that doesn’t end up down the drain. Unfortunately, those chemicals might be carcinogenic, so while it's a-OK to pee on them, please don’t slice yourself a delicious piece of urinal cake.
[h/t Laughing Squid]