When Jodi claimed she jumped up to that very high far corner of the shelf to retrieve Travis gun, that was her total undoing.
First, the jury realizes Travis never had a gun because he would have had box of shells, a gun cleaning kit, and a holster (think jodi even claimed this too).
Secondly, every juror is looking at that tall shelf in the picture and realizes how hard it would be to get up there especially with someone chasing them and they realize she probably would not have had the time to make it up to that spot the way she claims.
Thirdly, the shelves were not disturbed and in a rush like she claimed something would likely have been moved.
Fourthly, the shelves may not have even supported her weight if she jumped up on them in a hurry.
Fifthly, and most importantly the coincidence of the .25 being stolen at Grams and that matched the shell casing on floor.
So in summary, it all comes down to this story is just not believable to common sense. This is critical because the jury realizes Jodi lied to them directly. This means she probably lied about other things too.
IMO, I feel this part of her testimony was a critical part in her undoing. She went way too far in her lies and this part is a perfect example.
ETA: Added the 5th most important reason above.
