Why do wintergreen Life Savers spark when crunched?
Extensive research concludes that wintergreen Life Savers will indeed produce impressive -- but small -- bursts of blue electricity when smashed forcefully between the teeth. This sparking is a type of "triboluminescence", which occurs when something is crushed or torn, the something in this case being the hard crystalline sugar that Life Savers contain.
When you explode the sugar crystals with your teeth, electrons (which are negatively charged) break free. As a result, the atoms in which the electrons were formerly embedded become positively charged. The free electrons frantically move around, looking for a new molecule to bond with. As the sugar crystals explode, nitrogen molecules from the air affix themselves to the broken surfaces. When the free electrons hit the nitrogen molecules, they emit invisible ultraviolet radiation, along with a faint visible glow. The UV radiation is absorbed by the wintergreen flavoring, methyl salicylate, which then emits the fairly bright blue light you see.
Note that virtually all crystal sugar candy, including peppermint Life Savers, will emit some visible light when crushed, although it's usually pretty faint. The effect was first described in 17th-century Italy, and since then it's been discussed in numerous papers and articles.