Babies systems are very immature - and everything that they do is new and feels weird and sometimes could even hurt a little. I read in 'The Happiest Baby on the Block' that some babies overreact to a normal intestinal reflex that happens when babies eat. Their stomachs give their lower intestines a command that tells them to squeeze when they start to eat so that their systems can make more room for more food.For some babies this squeezing feels like a punch in the belly.