Hissing Ball?

[BonnieBallPython]

hello! i own a female ball python, about 8 weeks of age. shes always been very friendly towards me. she lets me pick her up, she lets me kiss her, old her close, and sometimes she'll let me restrain her (holding her still while i look more closely at her. i dont do that often). sometimes, she'll even slither into my clothes. anyway, to the point.
today, i was sitting indian style/taylor style on my bed. i had Bonnie, my snake, out and she slithered between my legs and into my lap. shortly after, i heard a somewhat "airy" noise. i brushed it off, but i heard it again and realized she was hissing. naturally, i was scared. i didnt move my legs out of fear of upsetting her, so i picked up my phone and called my friend, who told me to spread out my legs. i did, and she hasnt hissed since. she has let me handle her after that. in fact, i have her sitting on my laptop as i type this.
tomorrow is her usual feeding day. i dont know if that could mean anything.
what i want to know is, why did she hiss?

[Stewart_Reptiles]

It's a snake, snake hiss whether there is an obvious reason or not.