There are two different versions.
Submitted by Tom Sulkowski
The reason why Boba Fett has an acute hatred of Han Solo is that there
was a bounty on Han that Boba sought to collect. He injected Han with a drug
that made him obey commands. Lando ambushed them and gave Han the antidote.
Then they injected Boba Fett with the drug and told him to disarm himself
and fly away in Slave I. This was in The Hutt Gambit, book two of the Han
Solo trilogy by A.C. Crispin.
Dengar was the one who saved Boba Fett from the Sarlaac. Boba Fett had blown up the Sarlaac and escaped, and Dengar found Boba half dead while looking for valuables from Jabba's sail barge. The two then formed a partnership. This was in The Mandalorian Armor, book one of The Bounty Hunter Wars by K.W. Jeter.
When films go into production, great importance goes to eyeline continuity. When the director and cinematographer decide an angle to block and light the actors, giving consideration to what's coined as the 180 Degree Rule for understanding the psychogeography from shot to shot, Boba Fett needed in fact to be facing right, to face the other characters, or the camera needed to be more left to give the illusion of facing right. When the edits were being made, Fett needed to reacting to the other side of the room. So they flipped the negative for those shots, thus making a relatively symmetrical Fett, except his helmet antennah, work for the continuity of the scene.

Originally photographed.

Actually released.
— Source: starwarsdotcom.com
Before the complete unmasking in Attack of the Clones, in comic form, Star Wars: Infinities ESB #1 shows Boba Fett in Cloud City without his helmet.
Fett's first appearance was in the Star Wars Holiday Special. It aired on November 17, 1978. His first comic-strip appearance was in The Frozen World of Ota.
Boba Fett is humanoid which means of human anatomy. For example, Correllians (Han Solo) are humanoid. There is proof of this in Twin Engines of Destruction, first appearing in Topps' Star Wars Galaxy Magazine #6 and later reprinted by Dark Horse Comics.
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