Plot hole: In the scene where Sam and Carly are attempting to communicate to the military through the UAV drone, Sam tells them all about the Decepticons' plan to bring Cybertron into our atmosphere. But Sam was never there when Dylan explained the plan to Carly, and there was no time for Carly to have told him.
Other mistake: In the scene where Laserbeak picks up Sam and drops him off the building, Sam smashes through a glass wall with a handrail. Earlier on, he climbs over this handrail. No way would he have the momentum to smash a metal bar.
Factual error: Cybertron is placed between Earth and the Sun, as you can see in the shots from outer space. But it doesn't see to block the sunlight, despite being notably bigger than the Earth. It may be a framework but it's very dense with multiple layers.
Revealing mistake: When Optimus uses the Shockwave cannon to bring down the cupola with the control pillar in it, the cupola starts falling before the bullet hits the building.
Continuity mistake: When Ironhide crashes into the remaining dreads and transforms, one of the dreads is shown falling into some kind of wooden box covered with glass breaking it apart. In the next shot the Decepticon stands up and the debris is not visible.
Revealing mistake: During Optimus Prime's rage the same red BMW gets flipped three times.
Continuity mistake: When Sam's parents first show up, we see a shot of their RV with a car parked behind it, on the pavement. When they go to use this car to take him to his interviews it is now on a trailer behind the RV.
Other mistake: When the Autobots return during the fight they say they were hidden in the first booster rocket to break off. When their rocket exploded the first boost rocket hadn't broken off yet.
Continuity mistake: When Sideswipe kicks the gun towards Ironhide, the latter one catches, turns, locks, aims and holds the gun still all in the same motion. The nest shot has him do the same again, only this time he keeps on turning.
Continuity mistake: When Optimus dives in front of Shockwave, there is all sorts of rubble around the latter one. In the shot of the bullet arriving at the cupola, all of the rubble, damage to the street and broken cars are gone.
Continuity mistake: Just before the soldiers jump out of the Osprey, there is a shot of them running for the exit. You can see a very big gun on the soldier's chest. But in every shot of them wingsuiting through Chicago, none of the soldiers can be seen carrying any kind of weapons, let alone big LMG's and assault rifles which they use after landing.
Continuity mistake: After Sam and Carly are reunited, her hand keep altering from being very dirty and in Sam's face, and clean in Sam's neck.
Revealing mistake: During the highway chase scenes there are two "out of sync" animation sequences of the Decepticons in action. 1) In the front view with all the cars facing the camera, the Decepticon robot on the right shoves the car sideways (to the right), however, the car flies into the air a second later and in the opposite direction. 2) The scene cuts to the side view of the Decepticon and you see him motioning to pick up a car and begin to toss it in the air. However, when he does this, his hand is empty and the car just flies just below him.
Continuity mistake: At the beginning, when Sam receives the medal , his hairstyle (parting) alters .
Revealing mistake: Megatron's foot (tyre) clips through the bottom of Lincoln's chair.
Visible crew/equipment: The camera crane is visible reflected in the glass when the army dudes are prepping a rocket launcher. This is the scene before everyone is sliding down the building.
Continuity mistake: When the Decepticon jumps into the leaning building, Carly ducks in panic. When the shot cuts, she is standing straight up again, very calm at that.
Continuity mistake: When the soldiers are wingsuiting into Chicago, they fly past Trump Tower multiple times.
Continuity mistake: When Starscream flies in to destroy the Ospreys with Lennox and his team, you can see that the streets below are pretty badly damaged. When the soldiers jump, there are a few shots from a helmet cam from one of the soldiers and the streets are completely intact.
Continuity mistake: During the Mexican Standoff, Ironhide finally forces the spike into the face of one of the Dreads and lifts him up by it. Pay attention to the red car underneath: when Ironhide smashes the Decepticon's face, the windshield is fine, but when he puts him down, the windshield is suddenly damaged - before the Decepticon lands.
Answer: the weapon is called an "Acid Rust Blaster" which seems to be similar to the cosmic rust seen in the animated series. the rust eats away at the Transformer's metal body.