The LEDs are lit up for the 15 seconds the tank is dead and while it's starting up again. The death sound is triggered at the beginning of this time, but can last as short or as long as the recorded sound is.
It would be possible to detect the longer period while the LEDs are lit, but not in a super simple fashion. I'd probably tack on a micro controller if I was doing it, or start a 555 timer when the LEDs are lit, and trip a relay when it finishes *if* the LEDs are still lit.

Ahhh...kids. Well, that's different.

I'll have to think about it a bit.

D.