Single use cameras with a flash have a photo strobe capacitor that can hold a charge even when the power to the circuit is taken away. If you take this charge through your chest, it could stop your heart and kill you!
This scenario is pretty unlikely, but a possibility. Usually, you will get a minor burn on the offending finger and a new appreciation of capacitors. Still, never trust a capacitor! When in doubt...discharge.
I use the "short out" technique to drain the charge from the capacitor. This is not
the best method to say the least. The proper way is to drain the charge through an appropriate resistor or load bank (like a lightbulb) as demonstrated here:http://www.ehow.com/video_4997784_discharge-capacitor.html
Just be careful and know where your fingers are and you should be fine!