Eggs at Easter are specifically a product of Christian doctrine:

• Eggs were classified by the church as meat
  
• So you weren't allowed to use them in Lent
  
• But the hens kept on laying.
  
• People didn't want to waste food by throwing it away
  
• So they hard-boiled the eggs so they'd keep till after Easter
  
• But there were always more eggs than anyone could resonably eat,
• So they gave them to the kids to play with