Caesar's wife Calpurnia has had a terrible nightmare. In the dream, she saw blood gushing from a statue of her husband like a fountain and a mob of smiling citizens bathing their hands in the blood. Calpurnia interprets this as a ghastly premonition; she's sure it means that something bad will happen to Caesar if he goes to the Senate on the Ides of March.
Calpurnia's not normally a superstitious woman, but even she's spooked by the nightmare. Added to that, she's deeply unnerved by all the weird goings-on that have been reported in Rome lately, such as a lioness giving birth in the street and ghosts rising from their graves and walking around screaming. All of these weird events seem to suggest that there's evil in the air. Combined with her nightmare, we can see why Calpurnia's so anxious to keep her husband safely at home.
But Caesar downplays the significance of Calpurnia's dream and the many grave omens that have appeared in recent days. It would be absurd—not to say embarrassing—for him to tell the Senators that he won't be able to visit them until his wife starts having good dreams again. Caesar chides Calpurnia for her "foolish" fears before departing for the Senate for his rendezvous with destiny.