very worried about my snake :(

[duroo]

i just fed my boa for the second time since getting her. the first time i fed her i fed her a medium rat and she ate it with no problem and quite quickly. upon buying i thought it might be slightly too small for her but i figured i would start off small. well i just tried feeding her a large rat, which is about the same size as her largest part, and things went wrong. she started eating it headfirst like normal, got all the way up to its largest part (near the hips, then suddenly she spit it all back out. she could have easily kept going, and i was simply sitting and watching her silently, not disturbing her in any way, but she just decided she didnt want it anymore??? why did she do this?? im very worried about her. does anyone know what i might be doing wrong??


btw, both times i fed her f/t rats.