Why might an archaeologist want to use caution upon excavating Shi Huangdi's tomb?

• Legend states that vats of poisonous liquid are poised to overturn on anyone who enters.
  
  
• We have evidence that several trap doors have been placed near the entrance.
  
  
• Legend states that crossbows have been arranged to shoot anyone who enters.
  
  
• We have evidence that the surface of many objects in the tomb are coated with poisonous substances.