This week’s episode of Doctor Who solved one of the current series’ enduring mysteries, with the much-teased early regeneration for Peter Capaldi’s Doctor revealed to be a trick used to test the free will of companion Bill (Pearl Mackie).

Of course, this isn’t entirely a surprise – despite this regeneration being shown in several trailers, few fans believed it was the real deal, instead assuming it would be some sort of fake-out still allowing Capaldi to later regenerate into a new incarnation (played by a new actor) for real this Christmas as was previously announced – but the whole sequence has left us scratching our heads for a number of reasons.

To begin with, we’re a little confused as to how the Doctor pulled it off. While it’s previously been demonstrated that regeneration is a voluntary, self-activated process by Time Lords (for example, The Master refusing to save himself in The Last of the Time Lords and Time Lady Romana “trying on” different bodies in Destiny of the Daleks), as far as we know they’ve never been shown to be able to start and stop the process at will, as the Doctor does in this week’s episode.

Sure, the Doctor and other Time Lords have sometimes lent a little regeneration energy when not fully regenerating – most notably 2015 story The Witch’s Familiar, when Davros tricked the Doctor into supplying the Daleks with the power – but this week’s demonstration is different, merely displaying the visual appearance of regeneration without the effects and then swiftly stopped by the Time Lord.

There could be an answer to this within the series itself, of course – the Doctor was gifted a new sequence of regenerations in 2013 episode The Time of the Doctor (having exhausted the usual 13-body limit), and he has previously implied that this new cycle might have different rules to his original one. Maybe those new rules mean the Doctor CAN start and stop regenerations at will, or give off the appearance of them without actually changing, and this was a trick he’d been waiting to try out on someone.

But even if that is all true, it’s still hard to know why he’d bother doing it in this situation. In the fake regeneration scene, the Doctor is trying to goad Bill to test whether she’s actually operating under her own free will or the control of the Monks, culminating in her shooting him to stop him working for the Monks any more.

After the shooting (with Bill only actually firing a gun with blanks), the Doctor begins to regenerate – but why would he? As far as we know, Bill has no idea what regeneration looks like or even that it’s something the Doctor does, so it’s unlikely to have helped sell the whole lie to her. Rather, it’s more likely to have made her think something weird was going on.

Sure, it could have convinced the Monks if they were watching in – but it was made clear that it was Bill shooting the Doctor rather than him actually dying that was the proof of her independence from the brainwashing, and so if she DID shoot him there’d be no need to trick them any more. It was Mission Accomplished, Bill was back on side and they could finally take the fight to the Monks.

Admittedly, the Doctor did question whether the fake regeneration was “a bit much” afterwards, suggesting that he was merely indulging his flair for the dramatic rather than engaging in anything that was useful to his plan, but really you have to look behind-the-scenes before the whole thing starts to become clear.

Because you see, when you think about it from a promotional perspective, the regeneration TOTALLY makes sense. With Peter Capaldi already announced to be leaving Doctor Who before this new series even started, what better way to seize control of the ‘Who is the next Doctor?’ and regeneration speculation and turn it to your advantage than to actually show Capaldi regenerating in a few of your trailers?

The public interest in the future of the series is re-invested in its present, websites and newspapers are bound to write about your trailers and you get to throw in a fun twist to an episode that’s sure to have fans deep in discussion on internet messageboards.

Oh, and you still get to have your proper, heartfelt regeneration this Christmas. Congratulations, Doctor Who – just this once, everybody wins!