Babies. They're easily amused. Usually by things that most adults do not find amusing. Like vacuum cleaners.  Seriously, as an adult, you look at a vacuum and think "ugh, I don't want to do house work". But, as a baby, you look at a vacuum and presumably think "giant funny sounding sucking machine!!! It's so funny!!!". I mean, I think that's what the baby in this video thinks, anyway.