But... (spoilers)

...when Jim Hart (masked) kills the guy who was attacking Janet and her father, he is disturbed and flees when we hear Tim calling "Janet!" and entering from the opposite doorway in completely different clothes!
They're almost in the same shot together; how can they be the same person?!
Did Jim Hart throw his voice, change his clothes instantaneously and tele-transport himself to the other doorway?

And just as importantly, what were Jess and Guitar laughing at?