Sheldon: You're not done with her, are you?
Leonard: Our babies will be smart AND beautiful.
Sheldon: Not to mention imaginary.
When Sheldon is web chatting with Amy, we can hear Amy talking, yet the bar at the top of Sheldon's computer screen indicates that the sound is off.
After Sheldon mentions a molecular sieve, they go over to 4a, their apartment. 4a is a kind of molecular sieve.