When Ethan's mother is suffocated in the van, the top part of her face is visible in one shot, but obscured by the plastic bag in the next shot.
In the cold open, the autistic boy's feet are cut up, leaving blood trails all over the shop floor. But when Liz and Dressler later talk to the child services lady, she tells them he is physically unharmed except for "a few bumps and bruises".
While the instant explosion from the taxi crash shown in Milton Bobbit (No. 135) (2014) was impossible due to the lack of a fuel source, the opposite error takes place here. The gun thug has poured a flammable material, presumably gasoline. This would place sufficient vapor inside the van to ignite upon a sufficient source. Tom fires a handgun repeatedly, many sparks are shown, yet there is no explosion.
When Noah Schuster explains to Reddington what happens to the kids he talks about their twelfth birthday, "the end of adolescence", when it's actually the beginning of it.
There is no single sign language. In the US, for instance, there are at least two distinct languages, which are different than sign languages native to English and Australia. Most verbal languages have at least one sign analogue, if not more.
There never has been a "Grossmann" in German mythology.
The prop "detonator" Gina Zanetakos uses to blow up the SUV used in the robbery is the same prop "detonator" found in the front seat of the stolen truck in The Caretaker (No. 78) (2016).
The "rock" water well is a paper mache prop that shows damage to the inside edge just after Theo throws his mother down it near the end of the episode (38.30)