 " Birthday " contains elements of funk @-@ pop , synthpop , and disco house . The song is backed by a " busy but buoyant " instrumentation featuring a " deeply rhythmic impulse " . Randall Roberts of the Los Angeles Times felt " Birthday " was a musically updated version of disco , achieved by replacing " cheesy strings " with " jerky breaks and synth washes " . Its " joyful " lyrics present the commemoration of her partner 's birthday as a metaphor for sexual intercourse . The bridge section of " Birthday " , which sees Perry singing " Let me get you in your birthday suit / It 's time to bring out the big balloons " , was found by Ben <unk> to resemble French duo Daft Punk 's works . 
