Our little raft crests the peak of the flume and we begin to plummet. Nana, naturally fearful that her long life is reaching an unexpectedly premature end, opens her mouth to scream. As she does so, two things occur at once. The first is that her natural parenting instinct kicks in and she becomes fearful that my younger brother (seated directly in front of her) is about to fall out. Her first thought is to grab hold of him to ensure his safety (the fact that is considerably heavier than her and would simply pull her overboard with him has not occurred to her). The second thing that happens is, as her lips are parting for the scream to escape, she can feel the Polygrip on her dentures loosening and the ersatz choppers beginning to ease their way forwards to freedom.
Torn between whether to save Grandson The Younger from a theme park based death or to prevent him receiving concussion from a set of dentures propelled into the back of his head at high speed, Nana spends the mercifully brief downward journey with one hand clamped on the Brother and the other clamped tightly over her mouth to prevent tooth escape. Bro does not fall out, the dentures are secure in their mouth-based incarceration and Nana has been too distracted to have a heart attack. Everybody wins.
Of course, if she had lost her teeth, we could have spent the entire homeward journey getting her to say, "She sells sea shells on the sea shore". And she would've, too.