Question: how do you know if someone is really dead?
Answer: Kick Them. OK, OK, don't kick the possibly dead body. ... 
Check for a Pulse. Hold your fingertips to the person's wrist or on either side of their neck and see if you can feel for any sign of a beating heart. ... 
The Old Mirror Trick. ... 
Shine a Light. ... 
The Sniff Test. ... 
The, Um, Other Sniff Test.