He filmed himself and his son in the mirror, while making questionable noises and getting his child to copy him.
When he makes a "mmmm" sound and sticks his tongue out, his son sure enough does exactly the same.
And when he says "oh yeah", the baby tries to make a similar sort of noise (although he can't quite form the actual words yet).
At the end it gets even cuter when the father and son face each other and start copying the noise the other one makes.
Ah bonding time, isn't it the best?