Have you seen... [laughing babies]

We are evolutionarily disposed to love babies.  And laughing with a baby is good for you.  That's why this guy has almost 200 million views.  It even has an entry in Wikipedia!.

Something about tearing paper must drive babies to laugh.  This one has made 24 million people smile...

 ...and this baby laughs so hard he falls over!

Finally, what happens when you multiply a laughing baby by four?