Thatâs brilliant!
Just an intelligent guess, but I suspect the rectangular fellow top left is the odd one out? 
Looks like the old woman/young woman optical illusion to me⌠so can be either.
Itâs brilliant, theyâre all one way up but move your eyes around and they all flip over. I canât see an odd one out, I can only see them all the right way up or all the wrong way.
I agree with Peter. Itâs the rectangular one at the upper left.
If you are only seeing one upside down you are not seeing the full picture.
Iâve looked, and looked , and looked again many times, they all look the right way up, al, the time. You lot must be nuts 
Itâs the best optical illusion Iâve ever seen, by far.
Sorry Mark(âyou lot must be nutsâ), youâre the one who"s flipped his lids 
âNot seeing the full pictureâ
That little rectangular chap can see you coming, Mat, and flips himself over to look like all the others. Itâs a cunning plastic plot to twist your visual cortex into knots. 
You have to be very quick to catch the rectangular kid, David. Heâs the leader, and gives the command to flip to the others. He knows some of them are slow to respond, so waits until theyâve all flipped before he flips himself, like a parachute instructor. The large round type in the middle looks like a novice to me, and maybe needs a bit of help to turn over.
As you say, itâs a brilliant topic, and James is very good at turning up these amuse-bouche dishes, if thatâs not a rather feeble pun 
Still donât see it, I must be disillusioned 
Youâre not the only one - they all look the right way around to me and Iâm definitely disillusioned (though not about pictures of plates).
Iâm not nutsâŚby changing the angle of view slightly they suddenly appear upside down, but Iâm not sure theyâre all upside down because by the time I cast an eye over the whole picture, they are the right way up again.
Exactly Chris: those pesky polypropylene persecutors have got you where they want you. Are you beginning to doubt your sanity? Saying youâre not nuts is a sign youâre not sure, that you are on the non-stick path to madness.
Shape-shifting lizards have nothing on these smoothies. Put your mobile in a bucket of water and go to bed with a bottle or two of Kentucky bourbon. Tomorrow youâll feel safe again. I know, Iâve got these buggers stacked.
Sounds like a planâŚ
Donât think of using a plastic bucket, though Chris. Canât be too careful! 
With me theyâre all one way or all the other. Itâs very clever. At first I thought it was a gif and that there were actually different photos but, no, itâs an optical illusion. Way back in the â80s I could also look at those pages of coloured dots that were popular then and see the 3D images that they created so perhaps the two things are linked.
Dare I admit that they all look the same way up to me ?
I think that you, me and Paul must be the only sane ones here