Why don't nettles sting your tongue?

Nettles sting because they secrete formic acid when you touch them, right? And if you fold a nettle correctly, you can eat it raw without it stinging your mouth. Presumably, the pores or whatever that secrete the acid aren't in direct contact with your skin when you do this but why when you bite down on the nettle doesn't the acid get released and sting you? Is there something in the nettle that neutralizes the acid when crushed?