Is it normal for babies to suck their feet?

Yes: By 6 months baby has gained enough crude control of arms and legs to explore them by mouthing. Fingers (by 4-5 mo) and toes&feet (by 6months) are readily available teething objects. Any mouthing at this age is considered a simple self soothing or self play. As the child ages, their interest in tasteing objects(to program their brain) can be troublesome. Bugs on the floor are fair game.

Yes: Babies explore their environment through each of their 5 senses - sight, hearing, touch, smell and taste. Since a young baby cannot see very far, she tries to put everything in her mouth to taste - even her feet!

Babies: Yep ! As already well stated , feet are fair game ( as is lots of other 'stuff' ' , which is why we watch them like a hawk !)