Yang Yi found the content of the wiretapping intriguing, yet it was a pity that he couldn't record the intercepted conversation. However, with him present, the inability to record didn't really matter, as he was certain he wouldn't misremember a single word of what was heard.
Planting a bug on Jethro was actually quite risky because Yang Yi did not know if Jethro would be searched or scanned for electronic devices when he entered. If discovered, everything would be ruined.
Yang Yi felt that it would be improbable for Jethro to be searched given his status when meeting with Corkdor, so he took the gamble, and it turned out to be the right decision.
The information overheard this time was crucial.