The woman making chocolates with Lucy was an actual candy maker from See's Candies in Los Angeles.
The woman playing alongside Lucy in the candy making scene was hesitant to slap Lucy and did so very timidly in rehearsal. Lucy told to woman to really go for it, but it was no use. When the cameras started rolling, Lucy decided to slap the woman much harder than she did in rehearsal in the hopes that the woman would slap her harder too. It worked and the woman really let Lucy have it.
Ricky slipping in the overflowing rice was unscripted. The first slip was accidental, but it received such a great reaction from the audience that Desi purposefully slipped twice more.
Fred refers to Ricky as 'Ricky Margaret McBride' after Ricky shows him how he has starched Lucy's stockings. Television viewers at the time would have recognized this as a reference to Mary Margaret McBride who was a successful radio personality and journalist who reached the height of her popularity and influence from 1935 to 1955. McBride often gave household hints when advertising products.
Elvia Allman (candy factory boss) was one of the favored performers who was frequently called upon to play different supporting roles in the series. When the format changed to The Lucy-Desi Comedy Hour (1957), she was finally given the recurring role of Ida Thompson.