If you look at Happy's boots, you will notice the heel on the boots change! First they have a black heel, then a layered brown heel, then they have a flat heel in the sequences when they go from the garage to the car being crushed.
Walter states that ballistics gel is a non Newtonian fluid, it is not.
(It would be utterly useless for replicating flesh if it was.)
Non Newtonian fluids changes state when subjected to pressure, ballistics gel is a liquid that becomes a gel when cooled and gel is not a fluid Newtonian or otherwise.
If it had been non Newtonian it would have killed them both by solidifying and containing the the explosion in the confined space occupied by their bodies.
Walter talks about the ballistics gel they used in Da Bomb (2016) to protect Linda from the bomb detonation. They didn't use ballistics gel, they used gelatin. Ballistics gel is a type of gelatin made to exact ratios to imitate the density of flesh.
At the accident scene, the eye hooks used to place the car upside down were still attached to the bottom.
Walter's ring shows the wedding band is on the ring finger, in the next scene shows the ring is on the middle finger, next scene back on the ring finger.