Another thread mentions a mouse exploding from a huge electrical shock, which I would’ve given a “dubious” smiley if I had a good one to use. Naturally, I thought of Scanners (link to still image).
Bodies can explode from gas build-up when their owners have left the building, as police officers and coroners can tell you. Discrete internal organs in the living can from liquid buildup. (Gas buildup also?)
But short of that exquisitely effective power to make someone’s skull explode just by looking at them, what could do it?
Excluding anything “obviously” explosive such as a mini-bomb, blasting cap, etc. Although particularly creative or sneaky ways to introduce them would be interesting.