Keep your eyes focused on the cross between the two images.
After staring at the cross, the familiar faces become pretty unfamiliar, didn’t they?
A redditor explains the science behind the phenomenon:
“What’s happening in the OP’s illusion is that the brain is selectively juxtaposing certain aspects of the individual features on the left with those on the right because you’re crossing your eyes forcing your brain to have to reassemble what it’s seeing. But your facial recognition is kicking in so it’s combining specific facial components not just whole faces or shapes, contours, etc.
There are people whose brains are damaged in the fusiform gyrus, resulting in a disorder called prospagnosia. They can see perfectly but cannot assemble faces so what they see is a collection of edges, colors, shapes and lines that their brain doesn’t put together as one object… and when asked to draw what they see, many of these patients draw a disconnected bunch of edges, colors, shapes and lines.