How do gallstones cause gas and bloating?

I want specific step by step explanation of WHY..

first of all,, there are no gallstones stuck in the bile duck and clearly no stone in the neck of the gallbladder,, there are 2 mobile small stones in the gallbladder .. HOW DOES THAT CAUSE GAS,, IT IS NOT BLOCKING THE BILE,, ???? WHYYY
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