20 Things You Somehow Missed In X-Men

This is so subtle it's scarcely visible in a screenshot, and only slightly more so in actual motion.

For the scene in which Mystique impersonates Iceman and convinces Rogue to leave the Xavier School, Iceman's icy breath is just faintly visible.

While on the surface this seems like nothing more than a fun flourish to remind us of Iceman's abilities, given that the movie is set during the midsummer and his breath therefore shouldn't produce visible vapor, it's more generally accepted to indicate that Iceman isn't himself.

Given that there's no guarantee Mystique creates a perfect replication of the people she mimics, in this case it's a subtle giveaway to Rogue that something's off.