Deliberate mistake: The "chest compressions" Diggle performs on Oliver at the beginning of this episode are laughable. He's barely applying any pressure at all, and his arms are almost straight out in front of him instead of straight down. I would have called this a character mistake since Diggle really ought to know better, but this is more of a safety issue than an oversight; real chest compressions tend to break ribs.
Phixius
6th Jan 2014