Polly and Ben develop the solvent weapon

The bottles collected by Polly represent the initial, discarded idea for delivering the solvent. Though Ben suggests using them to throw the mixture, he quickly dismisses this in favor of fire extinguishers. Their presence in the scene underscores the improvisational nature of the companions’ plan, as they scavenge whatever is available. The bottles symbolize the raw materials of rebellion—ordinary objects repurposed for extraordinary ends—before being superseded by a more effective solution.

The fire extinguishers emerge as the solution to the delivery problem, proposed by Ben as a way to pressurize and spray the solvent mixture. Their red metal cylinders and hoses become the vessel for the 'Polly cocktail,' transforming safety equipment into weapons of resistance. The extinguishers’ practicality—already present in the sickbay, designed for emergencies—mirrors the companions’ own role as improvised defenders. Their repurposing marks a turning point, as the sickbay’s mundane tools are weaponized against the Cybermen’s invasion.

Acetone serves as the catalyst for the entire event, its dissolving power on plastic demonstrated by Polly as a proof-of-concept. Initially referenced as 'nail varnish remover,' it becomes the cornerstone of their weapon strategy. Ben’s confirmation that it is 'something like acetone' validates its potential, and Polly’s experiment—dropping plastic into the solvent and watching it dissolve—proves its efficacy. The object’s role evolves from a household item to a critical component in their improvised arsenal, symbolizing the shift from passive observation to active resistance.

Benzene is one of the solvents listed by Polly as part of their improvised 'cocktail,' identified alongside ether and alcohol. Its inclusion reflects the companions’ willingness to combine volatile chemicals in a high-stakes gamble. Though not tested individually, its presence in the mixture underscores the desperation and ingenuity of their plan. The solvent’s industrial strength symbolizes the high risk of their experiment, as they prioritize effectiveness over safety in the face of the Cybermen threat.

The piece of plastic dropped into the acetone by Polly serves as the critical proof-of-concept for their weapon strategy. Its rapid dissolution demonstrates the solvent’s potential to weaken the Cybermen’s chest units, validating Polly’s theory. The object’s role is purely functional but symbolically pivotal, as it bridges the gap between scientific curiosity and tactical innovation. Its destruction in the experiment foreshadows the Cybermen’s own vulnerability, turning an ordinary lab test into a moment of narrative hope.