She threatened to cut off my head?

My girlfriend (28) and I (23) had an argument for watching movies. I did not get angry but I said I was tired of watching her 'horror shit' and she said that if I talked to her again like that she'd cut off my head. I know she likes being edgy, but this made me feel extremely uncomfortable, she said it completely deadpan serious. Now she has a apologized and said she did not mean it, but I can't forget the absolutely icy glare she gave me when she said that. What should I do?
She threatened to cut off my head?
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