The two premises do not connect "balloons" with "dangerous", so the reasoning is invalid.
In everyday reasoning, the fallacy of four terms occurs most frequently by equivocation: using the same word or phrase but with a different meaning each time, creating a fourth term even though only three distinct words are used.
[2] For example: This EAE-1 syllogism apparently has five terms: "humans", "immortal", "Greeks", "people", and "mortal".
But it can be rewritten as a standard form AAA-1 syllogism by first substituting the synonymous term "humans" for "people" and then by reducing the complementary term "immortal" in the first premise using the immediate inference known as obversion (that is, the statement "No humans are immortal."
Consequently this common error itself has been given its own name: the fallacy of the ambiguous middle.