To truly understand the concepts involved with this activity -- get out your word processor and start typing your thoughts --- and in two or three hours --- YES --- HOURS --- they should be pretty well honed. Hopefully -- correctly so.

Students often say they want to "change schools" and "make children think."
This is a lie.
Very few pre-service teachers want to do that because it means they would have to "think," first -- and that would require sitting at a word processor -- typing their thoughts about the egg in the bottle for several hours . . .

Isn't there an easier way to teach thinking -- like WITHOUT THINKING ?

No.

Learning is not fun. It is an adventure.

to help get the water balloon / egg into the bottle, you can fill the bottle first with hot water; drain it, and quickly set the egg atop it.

why does this help the process ?

after doing the above you want to accelerate the movement of the egg into the bottle, what could you do without pushing it in ?

terminology:
air atoms and air molecules do not exist, and you should use the term, air particles, instead. Why don't air atoms and molecules exist ?

to err is human
someone says that the balloon / egg goes into the bottle because the flame of the burning paper "uses up the oxygen." Explain why the oxygen isn't "used up ?"

constructing answers
explain how using another method of getting the egg into the bottle would help children construct "a proof" that oxygen isn't used up when a flame is used.

show me
describe a safe ( no flame ), activity other than balloon or egg in bottle where students experience the effects of heat on the behavior of air particles.
Sketch a diagram on the back if you wish. ( p.s. you did this in class )

to err is human
someone says the balloon / egg gets "sucked into the bottle." This idea is false. Explain. The egg is not "sucked into the bottle" because

egg in the bottle -- a little help
the kinetic theory of matter has several statements that help us explain the behavior of matter that is seen in the "egg in the bottle" activity.

what are two of these statements ?