a fly on the wall

Translations
невидимый наблюдатель
I would love to be a fly on the wall during their meeting.
Я бы хотел быть невидимым наблюдателем на их встрече.
Definitions
A person who observes a situation without being noticed, often to gain information or insight without influencing the events.
Words
fly

noun
муха
wall

noun
стена
fly on

verb
лететь на