When is a fertility vase of the Ndebele tribe not just a fertility vase of the Ndebele tribe? When it represents Cady before North Shore sunk its claws into her.
The vase symbolizes her old, uncorrupted self, the one she officially buries—or, technically, hides under the sink—when she throws a small get-together that turns into a huge party…and one of her worst nights ever.
We're not saying the vase is cursed or anything (that's more Regina's game), but once Cady stashes it under the sink, her night gets worse and worse. She just keeps missing Aaron, which makes her anxious, which makes her pound shots. (Never a good idea.)
Later, she accidentally insults Aaron and then vomits on him, just as Regina walks in. Finally, Janis—whose art show Cady blew off to try to mack on Aaron—shows up and gives Cady a verbal smack-down for the ages. None of this would've happened to Cady 1.0. Burning bridges and barfing on boys are the handiwork of Cady 2.0, the Plastic version.
After the party, Cady forgets about the vase, a subconscious move that suggests her complete transformation into Plastic Cady. Then her mom finds it, chucked under the sink. Whoops.
Check out the conversation that follows:
CADY'S MOM: Why are my tribal vases under the sink?
CADY: I don't know.
CADY'S MOM: This is the fertility vase of the Ndebele tribe. Does that mean anything to you?
CADY'S MOM: Who are you?
Cady's mom knows what we're talking about. The Cady she knows—or thought she knew—would never toss the fertility vase of the Ndebele tribe into some cupboard. The Cady she knows would show some respect, and would think about others.
Unfortunately, for dear ol' Mom, at this point in the narrative, the Cady she knows has been hidden away deeper than any vase, fertility or otherwise.