Why Katy Perry was wearing light-up devil horns at the Grammys

If you tuned in to the Grammys Sunday night, you may have noticed Katy Perry and pal, singer Ferras, sporting a pair of devil horns at the start of the awards show.

The next time we saw Perry, the horns were noticeably gone, but many fans and viewers online were confused by the look.

What was the deal?

The horns weren't Perry's idea.

The horns went along with the AC/DC performance of "Highway to Hell" which opened the show.

Look closely and the horns say AC/DC on them.

It looks like all audience members at the Grammys had their own pair of light-up horns on their seats.

Take a closer look at one of the other photos of Perry again, and you can easily notice dozens of people in the background sporting the light-up devil horns, too.

There's a good reason you didn't see the horns for the rest of the show or on other celebrities. 

The Grammy show politely banned them from being worn during the rest of the awards ceremony. 

A message on a prompter read, "Ladies & Gentlemen: The devil horns are yours to keep, but please put them away for the rest of the show. Thank you."

Perry, Ferras, and others were left stashing the horns underneath their seats or on their laps for the remainder of the show.