Ms. Frizzle is picking up the seaish rock with BraveBean's beanie. Cuegan are watching.
… the title text?
Spoiler:
It's “LOOK OUT!” again. (BraveBean's beanie is contaminated. If Ms. Frizzle touches it at the wrong place or takes a deep breath she can easily pick up some plutonium oxide. Let's hope that she acts like a pretty big tree.)