Wash the vegetables: Rinse all the vegetables under cold water, then pat them dry thoroughly with paper towels. Removing surface water keeps the vegetables crisp and stops them from watering down the dip once arranged.

Cut the vegetables: Cut the carrots and celery into finger-width sticks, and trim the broccoli and cauliflower into small florets with a bit of stem attached. Slice the bell peppers into strips and the cucumber into rounds.

Mix the ranch dip: In a medium bowl, stir together the sour cream, mayonnaise, and ranch seasoning mix until smooth, about 1 minute. Taste and adjust seasoning if you like a stronger herb flavor.

Chill the dip: Cover the dip and refrigerate it for at least 15 minutes so it firms up slightly. A chilled dip holds its shape better once spooned into the bowl.

Set up the cauldron bowl: Spoon the chilled dip into a small black bowl or cauldron-shaped dish. Place the bowl in the center of a large serving platter.

Make the tomato eyeballs: Halve the cherry tomatoes and press a thin sliver of black olive onto the cut side of each half to look like an eyeball's pupil. Set these aside near the dip.

Arrange the vegetables: Arrange the carrots, celery, broccoli, cauliflower, cucumber, and peppers around the cauldron bowl in loose color-grouped rings. Fill gaps so the tray looks full from every angle.

Add the eyeballs: Scatter the tomato eyeballs among the other vegetables, cut side up, so the pupils are visible. Place a few closer to the bowl for a spooky peek into the cauldron.

Serve: Bring the tray to the table right after assembling so the vegetables stay crisp and cold. Provide small spoons or a butter knife near the dip for easy serving.