ARTHUR: David killed Goliath with a stone, right? GRAMP: Right.
ARTHUR: Wrong. Goliath was a GIANT. Which means he probably had "acromegaly" ...the body produces too much growth hormone, creating a HUGE human being. But the heart can't keep up, and eventually just gives out.
GRAMP: So, David killed Goliath...? ARTHUR: ...By making him jog a little.