Dr. Osaka, the organic chemists, is shown in her lab wearing flip flops and capri pants. In any lab where chemicals are mixed, open toed shoes are prohibited, and long pants or skirts must be worn to prevent possible injury from chemical spills, etc.
Alan refers to tunnels under Hollywood providing access to water mains as being related to the historic Red Car streetcar system. The only Red Car tunnels were in downtown Los Angeles.
As Liz is saying goodnight to Don at the end of the episode, behind her is an extra waiting for her to start leaving her cubicle before he starts walking to exit after her.