The Doctor and Susan are able to escape the sink using the plug chain, but in the cliffhanger at the end of the previous episode the plug was placed on the bench next to the sink after the sink had been emptied.
However, in the reprise at the start of the episode, the plug is clearly seen to be dropped back into the sink.
If the proportions of the miniaturisations are accurate, when The Doctor states that "that dosage of insecticide will be seventy times less", that is an enormous underestimate...the true reduction would be in the order of 1:300000.
The giant can of insecticide is labelled "insectide".
Alan Tilvern flubs the line "as soon as they get the report, we'll get the go-ahead."
After Forester asks for the authorization to be sent in, a boom mic is visible above Smithers.