How to blow up a cake? :D?

ksoo my dad bday is on june 30th and i wanna make him a prank cake that will explode but wont harm him, and hopefully wont make a big mess! anyone know any ideas to blow up a cake? :D ( ps. my dad is a prankster so thats why im doing this, he will probably prank my back but it will be fun pranking him :D )