When Don sees his future death in the Witch's eye, it makes you wonder how it will affect him later. Even Edward admits that seeing your own death "could kinda screw you up", but this is never brought up. Then again... later, Don shows that he's so desperate to marry Sandra that he'll beat Edward to a pulp for intruding on her, even though Sandra obviously doesn't love him and leaves him for Edward at the drop of a hat. Why is that? Could it be that he knew he was going to die soon, and was terrified of dying alone? Tragically, Don's desperation to avoid this ends up leading to his death.
Edward's story about how he learned the giant catfish was a pregnantfemale isn't as arbitrary as you might think. Given he made up the story to make up for missing out on Will's birth, Edward might've put that element in the story so he could metaphorically feel closer to his wife and son.
Will's speech about ice burgs takes on a whole new facet when you realize he's Right for the Wrong Reasons. He has been only seeing 10% of who his father is, and his tall tales have been keeping him from seeing the whole picture. But rather, it's in the context that he's been blinded by his prejudice of his father being a self-absorbedattention hog, rather than the Humble Hero who uses his stories to glorify and remember the people he helped throughout his life.
According to Tim Burton, the scene with Edward Bloom planting an entire field of daffodils for Sandra wasn't CGI, it was all real. Whether this was intentional or not, it fits in with the theme of the story: that despite Edward's stories coming off as outlandish, they were all real.
The story about Edward catching the catfish on the day of Will's birth is the very first story that we hear, and it's treated as a sort of Establishing Character Moment for both Edward and Will. Edward keeps telling it up until Will's in his 30s, even whipping it out on Will's prom night and at his wedding, giving the impression that he's self-centered and oblivious to his son's coming of age. We see Will gradually getting more annoyed at the story as he gets older, eventually accusing his dad of being a pompous glory hound who hides behind elaborate fantasies because he can't face the real world. But then at the end, we find out that the catfish story is, in fact, one of the only stories that Edward completely made up—all of his other tall tales were just exaggerated retellings of things that actually happened to him. The story then takes on a completely different meaning when you realize that Edward romanticized the story of his son's birth to make up for not being there to see it. He wasn't telling the story out of ego...he was telling his son how much he loved him in the only way that he knew how.
Regarding the exaggeration in the stories, how much is from the way Edward tells it and how much is from Will's imagination? For instance, if Edward mentioned the Siamese twins, Will could've pictured conjoined twins when really they were just twins from Siam. Or in regards to Karl, pretty much anyone would call an almost eight-foot-tall person a giant, but a child would picture someone called a giant a lot bigger than just eight feet. That doesn't explain the werewolf, though...
Theory: Amos Calloway was actually an alcoholic, and Edward Bloom found him while he was on a violent bender, but instead of attacking him or turning him in, took care of him for an evening so he wouldn't hurt himself. When Edward related the story to his son, he changed alcoholism to something a bit more child-friendly.
Also its possible that Amos had hypertrichosis, also known as werewolf syndrome.
The twins are "joined at the hip" in the flashbacks. Edward could have simply used the popular expression, while his son mistakenly thought he was being literal.
Edward was an accomplished storyteller. As such, he would have known the evocative power of Exact Words. To say something like "Siamese twins" would be a simple and effective way to paint the picture he wants in listener's mind (i.e., he knows how the listener would interpret the phrase) without veering into an outright lie.
It's also entirely possible they were conjoined, but only to, say, the degree of the Bunker or Hilton twins, both pairs of which were easily medically separable (Bands of tissue and some bone at the stomach and back, respectively), especially once Edward got them to the States, or when they retired from show business.
At the start of the film, there's a whole lot of fantasy elements involved in Edward's stories. Towards the end, closer to Edward getting into old age and the life of his son Will, the fantasy elements begin to decrease. The further away the stories are from the reality Will knows, the more outlandish they seem to him and the viewer, while those closer are still built on strange coincidence but not as out-there.
