Microbiology.

His new girlfriend must be on the way.

Enjoyed the episode but…
…did anyone else notice it contained a scene almost identical to a past one? Sheldon thumbing through comic books saying "got it, got it, got it…" although the last time it ended with him meeting Howard in the middle. And then Stuart disappointing him with a spoiler about the new Flash…

"Sign here" was indeed said plenty of times.