Myklebust had never held a gun before, and repeatedly managed to drop the ammo magazine while filming, leading to both cast and crew tearing up.
In the shot where Olly is eating a candy, he already has two in his mouth from the earlier takes, as he couldn't manage to chew them quick enough for the reset.
The woman in the wheelchair was asked on set if she could play the part, as the original actor quit hours before filming started.