Why does brake fluid squirt back into reservoir when applying the brakes?

When you apply the brakes, the brake pads clamp down on the rotors, generating pressure in the brake lines. This pressure pushes the brake fluid through the system, but as the brake pads make contact, the volume of fluid in the calipers decreases, causing the brake fluid to be displaced back into the reservoir. This is a normal function of hydraulic brake systems, ensuring that the fluid level remains balanced and that the brake system operates effectively.