So did our favorite bounty hunters meet their ends in Session #11? What was that... thing?!

When Spike tried to identify the monster he found, a healthy bacteria called Bifidobacterium turned up, a near mirror image of the mysterious substance.

According to Alicia, a vigilant fan who studies organic chemistry, most organic substances are arranged asymmetrically. Since the the digestion of food involves complicated chemical reactions between food and asymmetrical substances in the body, there are notable differences in taste, smell and digestibility of mirrored substances most of the time. The Bebop may have encountered the opposite of bifidobacterium, which may be  fatal after all. Bifidobacterium controls intestinal pH levels. The opposite of bifidobacterium would probably cause excess acid buildup.
 

Are Julius from Session #12 and Julius from The Movie the same person?

Though they share certain... eccentricities, whether or not the Julius from the Callisto migrated to Mars is up for debate. Though a similar character makes a brief appearance in another series.

Who sent Faye the beta tape and deck in Session #18?
 
One theory suggests the tape, a time capsule, became a historical artifact, randomly sent to various people in the Solar System. Yet another theory suggests an ex-boyfriend sent it to repent for past crimes. An old classmate may have sent it as well, hoping to find her after her disappearance.
 

ENLARGE
 

Flashback sequences in Session #5 and Session #13 briefly show one shot of a Red Eye vile and spray in  Julia's apartment. Who was using it?

The popular vote goes to Vicious. Thanks to Michael Wayne for sending in this one.

Did Bull know Spike's fate since Session #1?

"You will meet a woman... the woman will hunt you... and then death." Bull may have been referring to Spike's final encounter with Julia.

Is Spike really dead?

Even though he managed to survive gunshot wounds and a dramatic fall from a cathedral window, the relentless attacks of a psychopathic killing machine and a highly-trained Titan War veteran with a deathwish among other near-death encounters, Spike believed he was "already dead" since Julia disappeared three years ago. His days on the "Bebop" were his purgatory where he lived aimlessly as if in a dream. In Session #26, when Faye asks him why he chooses to die, he tells her that he intends to find out if he is alive. In the end, he finds out that he was "dead" all along.