Question about prototype


if I modify
“Dog.prototype.isPrototypeOf(beagle)”
to
“Dog.prototype.isPrototypeOf(beagle.prototype)”,
it turns out wrong, and if I modify
“Object.prototype.isPrototypeOf(Dog.prototype)”
to
“beagle.prototype.isPrototypeOf(Dog.prototype)”
it turns out wrong, too, why? Anybody can help me with this?

Challenge: Understand the Prototype Chain

Link to the challenge: