What is this?!

So on thursday i had work at six thirty.
I left my apartment at 6:15
My roommate got home around 7:30
I come home from work at 10:15 and there is this weird spiky ball plant thing on our dresser.
So later that night my roommate asks me what it is.
So i say, "I thought it was yours..."
She thinks it's mine. So we ask our other roommate if she put it there.
Nope.
WHAT THE HECK?!?!?!
Who was in our room leaving this weird thing on our dresser?!