Twistmas Advent Calendar (Part 1)
Created by Dr Matt Pritchard
At the end of 2025, Dr Matt Pritchard created an advent calendar for us consisting of 24 videos featuring Christmas illusions, curious objects and magical effects. On this page (and in Part 2) we’ll give further details on what is happening in each video and some additional ideas for you to explore. We suggest you watch this video before you read about each day individually below.
Day 1 – Christmas Tree Baubles
The Christmas tree baubles are all grey in colour. However, by being overlaid with coloured lines, they appear to take on that colour. The diagram shows one bauble at three different scales. You may be able to see grey in the largest of the three but as they get smaller, they appear to be pink in colour.
This effect is commonly called the Confetti illusion. Although a variation on the Munker-White illusion might be a better description. David Novick popularised this effect in 2018. He was inspired by the work of Akiyoshi Kitaoka. You can read more here.
Twist Museum has a demonstration of this colour assimilation where the famous Vermeer painting “girl with a pearl earring” has been printed in greyscale and then overlaid with a grid of coloured lines. From a distance, the painting appears to be fully coloured.
Day 2 – A Festive LEGO Transformation
No sneaky edits or digital magic used to create this LEGO illusion. We’re keeping the workings of this a mystery but many of the exhibits at Twist Museum rely on the properties of light, and this trick is no exception. How do you think it works?
Day 3 – Shepard’s Gift Boxes
Will the lid of the red present be able to fit exactly on top of the gold present? Surprisingly the answer is Yes! This is called the Shepard Table illusion after the psychologist Roger N. Shepard who originally published it as two tables. The 3D depiction of the boxes causes the brain to misjudge the shapes of the two parallelograms that make up the lid of the boxes. The shapes are actually the same albeit rotated. For many other illusions that rely on ambiguity and strange properties of shape, the book by Roger N. Shepard “Mind Sights” is recommended.
Day 4 – The Sleeping Snowman
If you have a third snowman and it’s lying down horizontally on the ground, will it be able to fit in the gap between the other two? The answer is no, even though it looks like there is enough or just enough space. This illusion highlights how certain arrangement of shapes makes it hard to fully judge distances without the use of a ruler. There are a host of optical illusions that can cause the brain to make wrong assumptions, many of which can be found on the walls at Twist Museum. Perhaps the most famous is the Müller-Lyer illusion that asks you to judge the length of two lines.
Day 5 – Christmas Jumper
The Christmas jumper illusion. It might appear from a distance that the lines on the jumper are changing shape from sharp zig zags to more rounded waves. However, the lines never change shape. They are simple sine waves. The illusion is created by changing the black and white shading pattern of the lines. The ‘phase’ of the colour pattern impacts how the line shape is perceived. The diagram below shows a few different arrangements. With the white and black lines at the peaks and troughs of the sine wave, the line appears more rounded.
This illusion is based on the Curvature Blindness illusion featured in Takahashi (2017) iPerception. You can read the paper here and a circular variation Dr Matt Pritchard made using this illusion principle can be seen here.
Day 6 – Tessellating Trees
A double illusion today. Firstly, there’s a ‘figure-ground’ illusion with the tessellating Christmas trees. You can either view it as a scene with dark grey trees that are upright or upside down light grey trees.
The main effect asks you to compare the trees labelled A and B. Are they the same shade of grey? They are! The illusion is created by using a gradient fill in some places rather than a solid colour. This creates a simultaneous contrast illusion where a mid-range shade of grey can appear light against a dark background or dark against a light background. Perhaps the most famous example of this is Prof. Edward H. Adelson’s Checker shadow illusion.
Day 7 – Odd Sock Out
Which of these Christmas stockings is the odd one out? This puzzle is based on a brilliant one shared by Guardian puzzle writer and author Alex Bellos. You could argue that it’s the red one. Or maybe the small one. Or the sock that’s facing the other direction. You may have even noticed that the last one doesn’t have a black outline. 4 out of the 5 socks have a unique feature. The only one that doesn’t is the sock on the left. Therefore, it’s that sock that is the odd one out. It’s odd because it’s not odd!
Day 8 – SNOW
Six sheets of acetate with what seems like a random arrangement of hexagons come together to form the word SNOW. The alignment is created by running threads through the corners of the sheets and pulling them all together. The construction was incredibly time consuming as Dr Matt Pritchard had to laminate the sheets without disturbing the patterns I’d laid out inside the clear laminated pockets.
Day 9 – Twinkling Snowflake
This snowflake made up from the shaded dots is not moving position or rotating. The only change is the shading patterns of the dots. Each dot goes through a sequence of 4 patterns (grey with shadows; black; grey with shadows on the opposite side; white) and that creates the apparent motion illusion. In the diagram, if these four dots were frames in an animation that repeated, the dot would appear to move to the right. By rotating the dots, they can appear to move in any direction you want. The snowflake animation made use of this to create the various illusory movements. Dr Matt Pritchard created an animation that’s similar to the retro game Snake.
More information about this fascinating effect can be found on Prof. Akiyoshi Kitaoka’s page.
Day 10 – Anamorphosis
Four examples of anamorphosis where distorted images are returned back to a recognisable state by viewing them in a curved mirror surface. Dr Matt Pritchard made the images by using a polar coordinate distort filter on a computer graphics program. Lots of options out there including free software like GIMP. You can download the Winter themed files Dr Matt Pritchard made here. Twist Museum has various examples of anamorphosis including a spooky sculpture that reveals itself in a wine bottle.
Day 11 – Duck-Rabbit Ornament
A wooden duck-rabbit illusion as a Christmas tree ornament. A 45-degree mirror allows you to see both animals at once.
Day 12 – Trees a Crowd
Which Christmas tree is the odd one out? A quick glance will often give the wrong answer. The tree on the right appears to be tilted further over than the other two. However, it’s the middle tree that has the odd angle. This illusion is based on ‘A turn in the road’ that was a 3rd place finalist in the illusion of the year contest. Created by Kimberley D. Orsten and James R. Pomerantz from Rice University. See the original here. Their version has added layers of deception as there is a perspective effect with the road markings.
Day 13 – Appearing Snowman
The snowman seems to appear from the water. It’s a curious bit of light science and how refraction changes the path of a light. On day 14 I’ll share a much simpler way to make it that doesn’t involve a laminator.
The diagram shows the various layers that are needed to create the snowman. You need to first draw a small picture that you want to vanish when placed into the water. Then cut out a thin piece of transparent plastic from some packaging. This is the same size as the paper. This is put on top of the drawing, and they’re then both put into a laminator pouch. Put the whole ‘sandwich’ through a laminator to make a watertight seal. Once it has cooled down, cut the pouch down to size and flex it back and forth. The key to the illusion is to have a thin air gap above drawing. Flexing the pouch helps to create this if the laminator has pushed the layers too tight together. Finally, using a permanent marker, draw extra details onto the pouch that you want to stay visible when underwater.
You’re now ready to place this into water. The illusion only works when looking down on the pouch, if you view it sideways there will be no vanish.
Give the illusions a go for yourself and share your creations with us on social media. Part 2 can be found here.
