The first time Arcane's thugs chase Alice Cable (Adrienne Barbeau) in the swamp, one of the guys shoots his own man and the squad leader takes his rifle away from him. After a quick cut away, the original shooter has his rifle back.
When Arcane's henchmen are drowning Alice Cable, soon after the "accident", Cable's hand reaches out of the water to fend off the attacker while the rest of her is submerged, but the hand is clearly that of a man's.
After escaping their cell and swinging thru the well to the swamp, Cable is deposited on the bank, her lingerie wet and clingy as well as her hair. Cut to Arcane flailing with the sword, and then cut back to Cable now sitting up on something, beautiful hair and gown completely dry.
When mutated Arcane has a sword and is fighting the Swamp Thing close to the end of the movie, right before Cable is stabbed, Arcane-Thing raises his sword overhead for a crashing blow down onto Swampie, and you can see that the monster suit has ripped in the armpits.
When Barbeau gets to the pay phone. The sound that's heard after she puts her money in the phone, is the sound that the phone company used to play when a phone had been left off the hook. The use of the sound dates back to the 1950's and 60's. It has since been discontinued.
When Jude and Cable are discussing the "tree" that Arkan's men's truck ran into, they look down at Swamp Thing's footprint and a white pointed toe shoe is clearly in the shot...however Cable & Jude are wearing black shoes.