I read somewhere that babies will laugh at their siblings before they react to other people. This was certainly the case when Elias was a baby. Only Joey could elicit big smiles and laughter from Elias. Now Elias is the champion at making Tanner laugh. While it doesn't take much to make Tanner smile, Elias posseses the power to generate big harty belly laughs from Tanner!
Here's video of Elias dropping toy balls on Tanner's tummy: