What is this and why won't my cat eat it?

[TheGirlOnTheLanding]

Sorry if this is horrible - look away now if you're squeamish.

BiteyCat is a proficient (though now more occasional) hunter. He's also very efficient - dispatches prey with hardly any mess or waste - but he always leaves the tail and one small kidney bean shaped organ which we often discover just before we tread on it. What bit of the mouse is it and why doesn't he eat it?

I can not for the life of me remember which bit it is but it is always left so he’s not usual in that.

Googling, I found I believe this thing is the cecum, which is the beginning of the large intestine

And I now feel somewhat nauseous.

Well I can see why he doesn't eat it although claws, teeth and various other bits don't sound that tasty either. It's all new to us as previous cat couldn't catch a cold.

Can't see a picture, but they tend to leave the spleen

Ooh my old cat used to always leave the same mystery organ too. Always wondered what it was. Current cat is too dim to catch anything.