Select the most appropriate meaning of the given idiom.

A fly on the wall

An unperceived observer

The most appropriate meaning of the idiom "a fly on the wall" is an unperceived observer.

This idiom is used to describe someone who is able to see and hear what is happening in a situation without being noticed. It is often used to express a desire to be present in a situation, even if it is not possible to participate.

The other options for the meaning of the idiom are not as accurate.

• A vigilant security guard is not typically associated with the idiom "a fly on the wall."
• A very intelligent person is not typically described as a fly on the wall.
• An unwelcome guest is not the same as an unperceived observer.