Throughout the movie the arm of the one-armed female doll torso switches sides. In some scenes the left arm is attached to the doll, and in other scenes it is the right arm.
(at around 5 mins) At the accident, when the fish tank starts floating, Rango has the glass in his left hand, but when he gets up and stares at the toy fish, it is in the right. In that same scene the doll's arm goes from left to right as well.
The bats' feet are reversed. Birds' feet curl backward, but bats' feet curl forward - exactly the opposite.
The clock tower is prominently shown to be a large (by their scale) ticking Telechron pocket watch, complete with company logo on the dial. However, Telechron never made either pocket watches or wind-up mechanical movements; their entire product line over 80 years consisted of electric clocks and related electrical timing devices, all powered by motors.
As mentioned, Rango's pistol looks intentionally like the Colt Peacemaker; whose action is advanced (cylinder rotated) by pulling back the hammer.
Colt Peacemaker cylinders are rotated by cocking the hammer; loading cartridges and removing fired brass are by opening a loading gate on the right side.
A Peacemaker's cylinder is never swung out to one side, as Rattlesnake Jake opened the cylinder to dump five shells out; leaving one shell in the cylinder.
Colt Peacemakers' simple mechanisms allow that classic Peacemaker single action look. Double-action revolvers, i.e. where pulling the trigger cocks the hammer and advances the cylinder, prevents double-action revolvers from ever having clean Peacemaker lines.
It appears the pistol as used is some amalgam of 20th-century double-action revolvers, stuffed into Peacemaker looks; an anachronism.
Rattlesnake Jake is shown blinking and narrowing his eyes. In reality, snakes have no eyelids - their eyes are permanently open.
(at around 1h 35 mins) When Rango stares down Jake ready for a gunfight, a dragonfly flies by and Rango catches it with his tongue and eats it. Dragonflies are located around abundant water resources and the town of Dirt is bone dry.
(at around 57 mins) At one point during the posse ride through the desert, an acoustic guitar is heard playing a solo, yet the mariachi guitarist is featured clearly playing a glittering blue electric guitar, complete with its power cord extending to the left off screen. However, the film is set in the modern day, Rango having previously fallen out of a car.
The roadrunners used for mounts by the characters make chicken noises. The dragonfly also buzzes like a bee or fly.
There are no natural Saguaro cacti in the Mojave Desert. They are native to the Sonoran Desert.
(at around 9 mins) Armadillo tells Rango to follow his shadow, which means he should be going opposite the direction of the sun, yet you see as Rango walks away that his shadow is pointing out to his right, indicating that the sun is to his left.
(at around 35 mins) While Rango hangs out in the Mayor's antechamber, he plays with a golf club, and knocks over a couple of actual golf balls that fit his character size. Yet when he plays golf with the mayor later (at around 1h 14 mins), they both use pill bugs as golf balls.
Rattlesnake Jake is in the habit of constricting like a constrictor rather than a rattlesnake.