Walter accidentally kills a cat in a wall with a knife, but when he takes it out of the wall, it is stiff, as if it has been dead at least an hour.
When the club owner knocks over the cat statue he notices the fur sticking out on the side. When he picks up the cat again the fur is gone.
When we see Walter's dish rack in the background, there is no pan for the blood. In the next shot, there is a big pan on the dish rack that Walter uses for Lou's dripping blood.
~ 10-12 minutes into the movie, Walter puts a pot on the stove but later when a close up reveals the contents are boiling over, it is a different pot & even stove.
Walter stabs the knife into the wall and it is at his chest height. In the next shot, it's up by his nose.
Decomposition would never allow him to get away with convincing people the victims were mere statues by simply covering them with clay, smell aside within only a few hours they would start to bloat thus cracking it and causing pieces to fall off.
Right before Walter punches the hole in the wall, the outline of where the hole is going to be can be seen before he breaks it open.
When Walter stabs the wall, the knife bends.
In the 39th minute Alice mouths several words to conclude her conversation, but there is no sound at all to match this.
When Walter and Carla are walking to the Art show, the shadow of a boom mic is visible on the bushes behind them.
When Walter unwraps the cat figure to show Carla, a shadow of the boom microphone is clearly visible in the lower right corner of the frame.