Element which best helps the audience create a mental image to make a speech more memorable is metaphor.
A metaphor is a figure of speech which describes an object or action that isn’t literal in its sense, but it helps in creating a comparison to explain an idea. It states the one thing to be another because they are the same in characteristics.
For example, he was unable to forget about the problems which were sinking his spirits like a lead weight.
Herein the lead weight sinks a fishing line similarly the personal life is getting low due to the problems.
