What is the purpose for that nasty little mat in the urinal?

At work there is a unisex bathroom that I don’t use often. It’s just icky. We have an actual “girls” bathroom which I usually use.

There is a wall urinal in the icky bathroom, and I noticed that there was some sort of small, flexible plastic mat in the bottom of it over the drain. It had spongy kind of spikes sticking up. What was it??? It was gross, whatever it was.