(Deliberate by filmmaker) During the pool scene, as April enters the water is played by Lindsay Lohan. After Machete enters the pool, the character is clearly not Lohan. This is because the footage is actually from the "Machete" fake trailer that preceded Robert Rodriguez's Planet Terror segment in Grindhouse - one of several pieces of trailer footage that were re-used in the movie.
The window next to the door in Luz's house changes between shots. In the exterior shot it's covered with cardboard or some other brown sheet (we even see the explosive bounce and fall to the ground) while from the interior it's a normal window with curtains.
When Booth is driving to pick up Machete at the day labor site, he is seen driving a Mercedes Benz S-Class (W220 1999-2006). At the day labor site, he is seen in a Mercedes Benz S-Class (W116 1972-1980). When he drives away, the car switches back to the W220 model.
In addition, in the inboard scene at 0:16:36 you can see the headrest of the W116 again. Later on (e.g. when Michael Booth gets his daughter from the house), the headrest is one of a W220 model.
During the monologue leading to the showdown between Torrez and Machete, two actors can be seen fighting behind and to the left of Torrez. During the dialog, they can be seen in and out of frame multiple times.
In the opening scene where Machete and his partner are attacking the drug-house, several bullets are fired through the windscreen as they approach the building. However, when the car crashes through the building, the windscreen is completely intact and bullet-hole-less.
In the beginning, when Machete pulls his machete out, it appears to have a ring near the hilt (Machete uses it to swing the weapon like a windmill). Later on, when he rescues the girl and she sticks to him, the machete has no ring in the handle.
In Spanish, the singular form of Federales is Federal, not Federale as constantly seen in the movie. Although this is a common Anglo misconception, it is presented on Machete's official personnel files which would never make such a mistake.
During the shootout at the church, Osiris Amanpour is holding a gun that tends to shoot like an automatic rifle (eg M-16). However this gun is a USAS-12 automatic shotgun with a 10-round-capacity box magazine. You can see shotgun shells ejected while watching in slow motion.
When the Padre is in the shootout with Von and his men, it's clear from the camera's angle that while the three men are looking for the Padre, and right before the Padre shoots two of thugs, Von can clearly see the whole side of the Padre hiding behind the column.
When the Padre is in the shootout with Osiris and his men, it's clear from the camera's angle that while the three men are looking for the Padre, and right before the Padre shoots two of thugs, Osiris can clearly see the whole side of the Padre hiding behind the column.
The goof items below may give away important plot points.
When Senator McLaughlin carjacks the taxi, the registration sticker clearly expired in 2008. Most of the other cars stickers in this movie didn't expire until 2010. This means the taxi would have been operating illegally.
When Machete impales Torrez in the stomach with his machete, it is initially seen exiting out his back. In subsequent shots the machete is still stuck in Torrez up to the hilt only no blade is exiting.
When the Senator is shot at the beginning of the film, it clearly happened in Austin near the Texas State Capitol. When the policemen are talking about which hospital he'll be going to, they mention Parkland, which is in Dallas, 200 miles away.
When Sartana's home is attacked by the masked goons, Machete fires nearly a dozen shots in quick succession with a six-shot revolver. This is a running gag in Robert Rodriguez films, which present an over-the-top, living-cartoon version of reality.
When the video of Senator McLaughlin shooting the immigrant is shown to the media, it plays as if it's been shot from three different angles (the same as the original scene from previously in the movie) instead of the single camera the thug was actually recording with.