“Then listen.
I am the murderer of Marie Cusheau.
She was my wife and she had cold feet and ate onions.
What was I to do?
Yet life is sweet to me.
I do not wish to be guillotined.
I have heard that you are on my track.
Is it true that the case is in your hands?”
------O. Henry
Tracked to Doom
http://www.literaturecollection.com/a/o_henry/130/
I think here "had cold feet" means be nervous/afraid or lose one's confidence, then what about "ate onions"? Does it simply mean the thing of eating onions? If it does, that is to say the murderer hates onions, and his wife's love of onions constitute one reason for his murduring. Is that right?