Four letters, starts with Oo and ends with s: Some 51 years after avant-garde artist Arthur Koepcke completed his artwork “Reading-work-piece,” which included a partially filled-in crossword puzzle and the suggestion “insert words,” a museum visitor followed his instructions.

The 91-year-old woman was questioned by police after she used a pen to add words—one of which was “wall,” per Deutsche Welle—to the Danish artist’s work at the Neues Museum in Nuremberg, Germany, the Telegraph reports.

“The lady told us she had taken the notes as an invitation to complete the crossword,” a police spokesman says. Museum Director Eva Kraus says the piece came to the museum from a private collector, who took news of the damage in “good humor.” Kraus says she realizes that the woman, who was visiting the museum with a group of senior citizens, didn’t mean any harm, but the damage to the artwork had to be reported to police for insurance reasons, the AP reports.

The piece by the late Koepcke, who was a member of the Fluxus movement, is valued at $89,000 and the museum believes restoring it will cost a few hundred dollars.

The BBC notes that, according to German paper Suddeutsche Zeitung, the elderly woman told police that the museum should have put up a sign telling people not to follow the artist’s instruction.

The woman who led the tour added that the fact that the museum has many interactive pieces added to the confusion. (Last year, art gallery cleaning staff tossed out an art installation depicting the aftermath of a party.)

This article originally appeared on Newser: Woman Fills Out Crossword, Screws Up $89K Piece of Art

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