I have always felt the only reason the Ramsey's brought up the cracked crab was because after they killed her they realized she had eaten the pineapple at home and they feared it would be discovered upon her autopsy. They needed the investigators to believe they carried her up to bed asleep, and never saw her alive again. Not knowing the pineapple in her stomach could be broken down and identified forensically, they knew cracked crab would resemble pineapple in the stomach, so they had to make LE think cracked crab was the last thing she ate.
Hmm, I'm not sure that is the way things went down. There is no evidence (even rumors) that says the Ramsey parents had any knowledge of digestive physiology.
Many folks have beliefs about digestion, but very few know the mechanics of it. Do you know that most vegetables and fruit leave the stomach before meat? Not because meat is harder to digest, but because vegetables and fruit are harder to digest in the stomach. Any fibrous veg and fruit can not be digested by stomach acid very well. It passes on to the duodenum (upper intestine) and continues the digestive process from there.
Meat is almost fully broken up by stomach acids. Which is why it stays in the stomach longer.
The pineapple in JonBenet's belly can tell us something about her time of death.