Rumors tell that he feeds primarily on new staff members and/or interns, which explains the perpetual glumness of those not currently eaten.
For them, bad news is often good news, and their glumness is self-evident.
He gave her a knowing twinkle, before lapsing into glumness.
Glumness apart, he nonetheless would like to be thought of as a comic writer.
What he needs to pull him out of this glumness is a new project.