system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does being tickled make us laugh?
gpt
I remember reading that one purpose of parents ticking their children is it teaches them defensive reflexes if they are attacked at different parts of their body (or something along those lines). Like puppies or kittens playing, it teaches them valuable life skills to survive. 

It makes you laugh / is fun because it is initially play. Parents wouldn't do it to their children if it hurt them or didn't get the positive feedback. So it is natures way of encouraging you to teach those reflexes to your children.