undeadTo celebrate Halloween, you may be tempted to visit a haunted house, take a spooky hayride or do another holiday-themed activity designed specifically to scare the bejeezus out of you.

However, there’s something important you should keep in mind when having frightening fun: Where you are in your cycle can impact just how startled you get by the loud and unexpected noises you hear, like a blood-soaked zombie popping out of nowhere and screaming his evil undead head off, the sharp “bang” of a cobweb-covered coffin suddenly slamming shut or hearing the eerie cry of a child ghost weeping in the foggy distance.

That’s the word from a study in the journal Behavioural Brain Research that found hormone fluctuations make you more likely to jump with surprise at unexpected noises during two phases of your cycle:

1. Ovulation (the last two days of your Week 2 and first day of your Week 3, which is Day 13 to 15 in a 28-day cycle): The researchers theorize that during ovulation, high estrogen is making your hearing ability sharper, allowing you to hear things you might miss in other weeks of your cycle. What’s more, the high level of this hormone is amping up brain arousal, which means you’ve got a lot more energy, which can make you antsy, anxious and, as this study points out, more easily startled by unexpected bangs, pops, screeches and wails.

2. Your premenstrual week: The researchers chalk it up to you being in a more negative frame of mind due to a plunge in estrogen, which makes you more aware of–and afraid of–potentially threatening situations.

So, what’s this ultimately mean for you?

Well, it can mean that you’re getting a lot more bang for your buck when you do scary Halloween activities during these days of your cycle.

Or, you could be flirting with a heart attack if you’re already especially jumpy. In which case, perhaps, a pumpkin pie eating contest or making a scarecrow would be more up your alley.