Recall the Time of No Return[Eng] - page 163

Rose, the Doctor has seen some shit. Of course this doesn't faze him. How about you be more useful than the actual Rose was and just shut up and let him do his work without getting in the way?

but but... he machine went ding!

This rings false. If he could detect zygons on sight, why didn't he twig to the two guards they just killed? Or every other zygon they've unwittingly walked past?
He also doesn't account for the possibilities of magic theft or psionic control. It'd suck to kill Twi only to find that she was being manipulated, wouldn't it?

Are you sure they haven't found some trick for being more convincing?

Hehehe. Wouldn't it be funny if Doc was a zygon? XD........ what?.....

The doctor could never tell the difference between zygons before. Why did he suddenly get this ability as a pony? 

Thank god, she's not the real one (maybe) but still, that makes me feel better 

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OKAY, thank you, that makes me feel better. At least he has a REASON for believing that she is not a zygon. I guess I can chock it up to the other girls being too in shock not to come to Rose's conclusion.

tmw you realize

the author had this planned all along...

So it all amounts to "because the doctor said so" and "the doctor is (almost) never wrong"? o_O

Convenient.... or is it? ^_°!

oh, well there goes my suspicion...

She could still be Chrysalis though, having a cooperation with the zygon.

Oooooh, I see!

I thought the story will go down the cliche path that Empress Twilight is an impostor. Good thing I was wrong, now I'm hooked to the story again.

Then maybe it's because YOU are a zygon doctor.

But Doctor isn't there a chance you could be wrong? Still can't wait to see what happens, great work.

Yet when he took out his machine.. It went ding...

.... You know with zygons you can't trust everyone so ..im going to spout out random ideas here.

1. Twilight isn't real like Roseluck said, meaning The Doctor found out something totally new in this world when it comes to the zygons and has trouble even accepting that he himself was wrong... When his machine when he first took it out went ding...((Come on .. Every one has a ego or some sort of pride why not The Doctor..))

2. Twilight is Real and the machine going ding was some of the gaurds around them being zygons and the machine is on the fritz like what happen in England with Queen Elizabeth.. The zygon was the horse not the queen thus.. This chaos just without a marriage proposal

3. Sometime when they were getting imprisoned in the dining room we did see Fluttershy black out it could be possible we only saw from her perspective this makes us wonder if they were seperated during the whole ordeal heading towards were they are....

Could be possible that either one of them is a zygon... Or possibly not. Which brings me to number 4 that may have a ton of backlash

4. The Doctor isn't The Doctor, and could be a zygon..

Though lets face it 4 is unlikely because The Zygons have to deal with all of his regenerations.. So its probally hard or nearly impossible for them to hold a Timelords form due to their complex structure.... And multiple regenerations Unless it is their First Face. The Orignal...

Thoses are my theorys have fun pondering