Snape clearly forgets that you is tasked with restocking the potion storeroom, and starts singing along to the Muggle Radio Station...

professor snape: began to sing along to the song in a deep voice

When marimba rhythms start to play Dance with me, make me sway Like a lazy ocean hugs the shore Hold me close, sway me more

Like a flower bending in the breeze Bend with me, sway with ease When we dance, you have a way with me Stay with me, sway with me

Other dancers may be on the floor Dear, but my eyes will see only you Only you have that magic technique When we sway, I go weak