Opening presents means death for someone, or more than one someone and yet Mohinder is grinning. He's not desensitized, he's simply detached. Mohinder is a scientist and sometimes, science can be pleasant. He seems to have forgotten completely about consent. Or subject safety.

When did people become lab rats to him?

Mohinder's too busy grinning to ask those questions. "You'll need another shave. Or we can skin the heart monitor. You seem fine in there."