The first scene that Edward James Olmos filmed as Castillo was the sequence where Barbara Carrow's body is retrieved from the river. Olmos later recalled in an interview that his response to Tubbs asking him whose side he was on was not scripted ("Don't ever come up to my face like this again, detective."), and that Don Johnson's disgusted reaction was real.
Castillo first displays his famous staredown in this episode, in fact using it several times - most notably directing his glare at Crockett, for not yet turning in his report on the bust earlier in the day, and Schroeder, for bursting into his office unannounced and verbally attacking Crockett.
According to Edward James Olmos (in Miami Vice (2001)), the reason there is a bottle of aspirin on Castillo's desk in this episode is because "everyone was giving him a headache!"