Question: When Seth teleports a plate with a piece of steak on it, why doesn't the steak merge with the plate?
Answer: Something non-biological can't merge with something biological.
Except that later on, a portion of the telepod merges with the Brundlefly.
Question: Well into the movie, Seth's computer, which uses voice recognition, can no longer recognize his voice due to his transformation. How then, did he hook up the three telepods and execute the final sequence if he couldn't get into his computer?
Chosen answer: He just used the keyboard. We see him typing on it several times before this scene, so the computer is not voice command only.
Question: Why exactly does Brundle experience a feeling of euphoria and strength after his teleportation? Why doesn't he turn into the Brundlefly immediately?
Answer: Brundle's just had all of his atoms separated and then joined back together with a massive influx of electrical energy; certainly that would generate some sort of sensation in cells that have never experienced it before. No reason to believe it couldn't manifest as euphoria and strength. As far as the transformation: Brundle's cells have been put back together with fly DNA in them, but with very little actual fly material, initially. It's reasonable to expect that as his cells die off and regenerate in the usual ways, they are replaced not by human ones, but by human/fly hybrids. As this happens, he becomes gradually more fly-like.
Question: What would have happened if Seth had successfully made the teleportation with Ronnie?
Answer: The deleted 'cat-monkey' scene (where Seth fuses the baboon he used for his experiments with a stray cat) sheds some rather unpleasant light on what would've happened. Essentially the telepods would've merged Ronnie, Seth, their child and the fly DNA together into some manner of chimera-like monstrosity that would most definitely not be what Seth had been hoping to accomplish. As if that wasn't bad enough, the film also implies using the telepods while clothed is a very bad idea (Seth strips naked before both of his attempts), so just imagine how Ronnie, being teleported with her skirt, sweater, stockings and shoes, would've further corrupted whatever resulted.
Answer: Actually, if the teleportation had followed through, then four bodies would have merged into one: Ronnie, Seth, Fly, Baby. Remember, Ronnie was pregnant.
Answer: Short answer, because the plate doesn't have DNA. Initially the pod was making synthetic versions of what was being teleported, which is why it turned the baboon inside out and made the steak taste funny but inanimate objects appeared OK. It was only later, after reprogramming, that the pods could basically identify tissue to teleport living organisms. However, with the fly present, the pod's programming couldn't distinguish there were two separate living organisms and ended up combining them. It didn't happen with the plate because the pod recognized it as a separate object.
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