Some parents look to Science to translate their babies' cries. This is a mistake.
The attentive parent will, with a little experience and practice, eventually be able to distinguish between his child's cries, and thus he can be confident that he knows how to soothe her.
Sometimes it might take a couple of weeks, as when your kid gets molars in ahead of schedule, and you only realize after the fact why she's been a whiny little mess.
But then, other times, such as when you catch her belly in the buckle on her high chair, you can know instantly.