Plus: Simon Cowell's out sick, the judges walk out and a contestant is arrested for lifting a mic
The superstar showed off her vocal talents by performing a classic tune, “Happy Birthday,” for co-judge L.A. Reid, who turned 56 on June 7, when the show was taped. (Watch the video here.)
It was a treat for fans of Spears, who rarely goes a cappella on TV.
He was replaced on the panel by Irish music manager Louis Walsh.
Wednesday’s episode also showed the taping in Kansas City where the judges first walked out of the auditions after contestant Deangelo Wallace performed a shamelessly bad version of “With You” by Chris Brown.
Wallace, 19, left with the $3,000 microphone and was later arrested by police.