Why does my mouth hurt when I eat pineapple?

I know that Pineapple has a high acidic level but when I eat it cut into pieces it doesn't burn. Only when I eat it straight from the skin does it sting. It makes my mouth numb, and it burns like I ate something hot. My hypothesis is that when i eat if from the skin the viens are leading straight to the skin wall, but when I cut it it cuts those veins, and it's not as "strong". Any help?