1) Partake of a sports broadcast 2) Snoop 3) Use a wiretap 4) Work with bugs 1) Uses a bug 
An actor must 'listen in' to the others on stage to gather the nuances of the language and action. It is too easy for an actor to reply automatically without considering the import of what they are saying. 
[v] - listen without the speaker`s knowledge 2. [v] - listen quietly, without contributing to the conversation