When Evil Calls centres around the mysterious appearance of a text message that grants the students at Willburn Hall their wildest desires. A-cup Alice wants bigger breasts, until her cup runneth over in an explosive mathematics class. Hilary would give her right arm to lose weight – and the blades of a kitchen waste disposal unit oblige. One by one, Willburn’s students learn a lethal lesson: be careful what you wish for.
Details voor de vertaling
Translators: Please read my note under the English original text! -- kafetzou
"my cup runneth over" is an expression meaning "I have more than enough", but here I think it also refers to something happening to her fake breasts (I haven't seen the movie, nor do I expect to).
"to give your right arm" is an expression that means "to want something so much that you would give up something that is important to you", but here I think they are mixing the expression with the literal meaning.