Continuity mistake: The tyres on the crotch rocket motorcycles they were riding kept changing from knobbly tyres to road slicks, back and forth depending on what terrain they were on. Easiest to see when Ethan skids on the road to avoid the white van - clear shot of slick tyres - then about 30 seconds later they're on the dirt, he skids into the old car and you can easily see that he's got off-road tyres front and back.
Continuity mistake: In the car chase scene with Nyah after they split and hit again and are spinning look at Ethan's car. The driver's side in the close ups was on the American side, then in the spin it is reversed to an English side. (It is a negative image - the license plate is reversed). The next image is back to normal.
Factual error: In the scene at the race track where they show the virus infecting and destroying cells in the blood stream, they clearly show that it is red blood cells being infected. Viruses, in order to replicate, require the cell's DNA replication machinery. However, mature red blood cells in the circulation no longer possess this machinery since they no longer have a nucleus or DNA. It would therefore be impossible for this virus to replicate.
Continuity mistake: The registration plate on Ethan Hunt's bike changes between 'NI 89' and 'ND 69' on occasion. Clearest moments are NI 89 just as he goes into the flames on the burning bridge, and ND 69 when he's through them.
Continuity mistake: In the scene where Hunt is chasing Nyah in the car, there is a part where he almost hits a gray car. When the camera shot comes from behind, we see a gravel road on the side with pine trees, but when it cuts immediately to an air shot, we see a concrete bridge-like road with no gravel for several feet ahead or behind. It does this throughout the scene.
Continuity mistake: During the fight between Ethan and Sean, Sean cuts Ethan's face with a knife and it's bleeding. A little bit later it is not bloody and it looks as if the wound is closed, then open and bloody again.
Visible crew/equipment: When the cars flip over as they blow up, you will see a circular object underneath the vehicles, about the size of a tyre (very obvious in slow motion). This is the device that "lifts" the vehicle for it to flip on one side, timed with the appropriate explosion.
Revealing mistake: During the scene on the beach just after the collision of the two bikes we see Scott and Cruise flying together in a big hug, but if you see the short shot when the black bike starts to explode frame by frame you will actually see a lonely man with his arms wide open.
Factual error: In the scene where Ethan is in the helicopter about to rappel into the BioCyte building, you see his hair blowing upward. In reality, the prop wash from the helicopter would make his hair blow into his face.
Continuity mistake: Why did Hunt's team decide to use an outback location as their Sydney base? It looks like it's in the middle of the Nullabor, which ain't exactly a helicopter ride from Sydney. Come to think of it, there isn't much terrain like that anywhere within a several hundred kilometres of Sydney.
Continuity mistake: When Ethan finishes showing Nyah the pictures of the aeroplane crash so she can see what kind of man Ambrose is, she puts out a candle with her hand. Then when they show her from the front, it's lit again, from the side it's out, then lit from the front, AGAIN!
Visible crew/equipment: In the scene where Nyah and Ethan have a race with a Porsche and an Audi-TT, at the end after the camera shows Nyah's feet you see both cars from front. Now on the right side of the screen you see the shadow of the filming helicopter.
Revealing mistake: When Ethan's pal is in the helicopter and Ethan is escaping on the motorbike he fires a grenade launcher at the car - he misses the first time, gets the car the second time, but you can clearly see the bridge is made of wood - where the car gets blown up there's a big concrete/steel plate to support the bridge.
Continuity mistake: When Nyah and Ethan are in bed in Spain, the lights reflected off Ethan's face and of the bed covers change between shots.
Continuity mistake: In the scene where Nyah is walking up towards Ambrose's house, the wind is playing havoc with Nyah's hair and scarf. Throughout the scene, there are several shots of her where there is no wind, her hair is not moving and the scarf is perfectly placed (most noticeably when she steps off the boat onto the walkway).