First reference to Rambaldi and first reference to Anna Espinosa.
The "prototype" car unveiled at the party is merely an ordinary Opel Speedster.
Plutonium is very heavy. A ball that size should be a visible strain to hold up.
The episode's title, "Parity," is a computer reference. A parity bit is an bit at the end of a byte used for error detection. Its association to this episode seems to be the relationship between Sydney and Lambert and his supervising of her progress.
The set in which the car is displayed in Madrid is the same set that was used in That Old Black Magic (1999) as a museum.