Revealing mistake: When Elliot appears in the fountain, after the sensitive guy segment, water is already up his trouser legs. (00:44:50)
Revealing mistake: In the scene when Elliot speaks Spanish, there's a mix of different Latin American accents, and what he is saying does not make much sense to a Spanish speaker.
Revealing mistake: During the opening sequence we see a lot of things happening very quickly and sped up. Everything is going in a progressive direction, not going backwards. As the sun rises in San Francisco a clock on a building is shown. The hands on the clock are going backwards instead of forwards. This was shot at dusk, not dawn, then reversed. (00:02:25)
Answer: It definitely is a Montegrappa Oriental Zodiac pen, this brand has been making pens in Italy since 1912. I am not sure which of the three red pens in that collection (Oriental Zodiac) is the one seen in the movie, but given its association with the devil, my guess will be it is the Ox fountain pen.