There is a rock in one of the wheels. It might be because a rover doesn't have pockets.

Someone has picked up a great rock, carried it around, saved it, or placed it somewhere special. The Perseverance rover has been carrying a random Mars rock in it's wheel for a long time.

There was a rock in the left front wheel of the rover. The rock has been with the rover for a long time. The rock isn't doing any damage, and the team thinks it has traveled more than five miles from its original location.

There is a potential down-side to the rock in the wheel.

A quick reminder that, for some time now, @NASAPersevere has had a rock stuck in its front left wheel.The rock doesn't seem to pose any problems.

But take a moment to think about the awful grinding noise that thing makes as it slides around every time the rover moves. pic.twitter.com/oqaxx1U66c