We have seen evidence of this a hundred times. They go into the plant and wander towards the main reactor. Mulder, I love ya, but there ain't NO excuse for sticking your fingers in the goop. Then he jumps a mile when his phone rings. I would have to say excited.
Teamwork is a lovely thing.
Next, Mulder and Diana see a man with Gibson. Being used again. Kidnapped from the hospital and out from under Scully's protective eye. Mulder has got to be pissed, and discouraged, by this developement. They go into the main reactor and lock the door.