This is confounding me. I set it to eavesdrop from the catwalk then go down the passage. I return to the catwalk and a big ear pops up. My cursor becomes an ear also. Now what? Clicking on the big ear makes it disappear, but I heard nothing. What am I doing wrong? I've exhausted the conversation topics with Larisa et all as well.

Did you get told by Larisa that this is where you need to listen first?
If so - try again from a saved game. It might get you over the hump.

Yes, I talked to Scott, Larisa and Dirac. I've done everything I was supposed to as far as I know. The big ear just disappears when I click on it.

Doh! I was eavesdropping on hall A instead of B. Never mind. Thanks, the all knowing and all seeing MaG.

Glad you found out what was holding you back. Have fun with the game.