We’ve seen plenty of weird and wonderful optical illusions here at Creative Bloq, but here’s one that hits a bum note – for all the right reasons. To celebrate Prostate Cancer Awareness Month earlier this month, charity Prost8 shared a cheeky billboard campaign with an important message.

“A prostate check isn’t what you think,” reads the tagline, which appears to have been slapped over a close-up photograph of a pair of buttocks. It’s only when reading the tagline that it becomes clear that this is a clever anatomical illusion. (Looking for more design inspiration? Check out the best print ads of all time.)