Playing games can be fun. Except when you don't know who you're playing with or the rules of the game.
And if you're ticking both those boxes, we're verging on the edge of creepy.
For TikToker Marc Sebastian, that has certainly been the case on board Royal Caribbean's Serenade of the Seas.
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Marc has been documenting his journey on the cruise ship which is sailing for a staggering nine months straight.
Marc is only onboard for part of the long trip, boarding the vessel for the 18-night South America to Antarctica leg.
Posting to TikTok, he's racked up millions of views for his witty and unique takes on the cruise lifestyle that is loved by so many. He is very much an outsider to the club; something he is embracing.
But one recent update shone a light on the games people play on cruise ships - and it left him a little bit weirded out.
Marc posted: "To whoever keeps leaving me ducks in secret, reveal yourself."
That's right. He's been bombarded with random rubber ducks and he doesn't know who they're from or why he's being given them.
Holding a blue rubber duck, he said: "Someone put this next to a bottle of water when I had walked away from my stuff once.
"Then this one [holding a turquoise rubber duck] was actually attached to the doorknob outside of my room.
"Which means you know where I live.
"I don't know how I feel about that.
"But this one [holding a yellow rubber duck] I was in the windjammer just reading minding my own business, and I'm always on high alert in the windjammer.
"I went to go get another pizza and when I came back this was on my book, so what's going on?"
Marc then ended the segment by smiling and said 'but honestly, keep doing it' while giving one of the ducks a squeak.
The TikTok comments were alive following the video, offering the best explanation they could.
One said it must be 'weird knowing people are watching you'.
A second said: "I saw from someone on another cruise it’s a thing to give small gifts to strangers. It’s got a name but it’s just a nice gesture. Like Jeep ducks."
Another added: "Those are cruising ducks hahaha. It’s like a whole thing.
"People buy bunches of rubber ducks before the cruise and then hide them around the ship for people to find. A lot of people collect them from different cruises they go on."
According to Cruise Radio, 'cruise Ducks have become the new trend on cruise ships, where passengers hide rubber ducks for others to find'.
It adds: "Though the origin and reasons for this trend are obscure, it has gained significant popularity among millions of cruisers."
So if you find yourself on a cruise and given a rubber duck, don't worry, you don't have a stalker. It's more likely someone just playing a game you didn't even know existed.
Tom Earnshaw