A hiker has gone viral for sharing a post-trek celebratory photo online but not just because he traversed a whopping 3,500 kilometres along the east coast of America.
The snap, which was uploaded to Reddit, shows a kilt-clad Patrick DeIvernois and three of his friends enjoying a well-earned whiskey after completing the epic Appalachian Trail.
"I swear there’s four of us," Reddit user 'Balrog Bunghole' captioned the photo in reference to the mind-bending optical illusion.
Can you spot it?
Indeed, there are four mini bottles of booze but only three arms visible...
So, is the fourth bottle floating in mid-air? Is Patrick's fourth trekking buddy a ghost? One thing's for sure, the pic left Twitter users bamboozled when it was re-shared on the platform.
"My brain refuses to believe there are 4 people in this photo," wrote the Twitter user who re-shared the pic.
"I'm confused... why are there only "3" arms, yet "4" bottles?" another asked.
Figured it out yet?
Here's a hint: look closely at the left side of the photo... yep, the fourth hiker is wearing a camouflage long-sleeved jacket making their arm blend almost seamlessly into the rocky background.
Back over on Reddit, users sheepishly admitted that it took them longer than expected to spot the phantom limb.
"Lmao. I was so confused for a bit there," wrote one.
"Yeah took me a solid 10 seconds until I saw the arm. Good camo," another added.
"I’m embarrassed by how long it took me," said a third.
"I actually saw this picture for the first time when my friends sent me a screenshot of the Reddit post.
"At the time of the photos being captured, I, as well as my friends, were unaware of the optical illusion that was present."