When I was a young lad, schools provided Bic pens to write with. They are not the usual pens you are used to, these pens were solid dark-blue, round in cross-section (not polygonal), and both the pen and the cap tapered gently. When capped, the cap almost divided the pen in half (i.e the cap was about 3" long). Also, the gripping handle was bumply, like a cobblestone road, writ teeny. I have been unable to find a pic of these pens online, so here is a sketch: Anyway, the thing about them is that, when you chewed on them (and you did chew on them), they would make your lips and tongue go numb and swell like you had a fat lip. It was a pretty dramatic effect for something that was supposedly safe for youngsters. They also tasted awful - bitter. What kind of plastic might that have been to make your lips and tongue go numb? It didn't take much. Even if you didn't chew them, and just stuck them in your mouth, wherever they touched you'd get numbness, a bitter taste and swelling (obviously, it was stimulating the erectile tissue of which your lips are comprised). I'm thinkin' some kind of PVC?