Personally, I feel that in most cases, thumb sucking should be allowed to continue. It is usually a benign habit that allows children to calm themselves and which goes away on its own when the child is ready to give it up. Hiccups are very normal and are related in some way to immaturity, probably immaturity of the nervous system. As far as I know, no one knows what causes them. They usually start before birth.
Most moms can feel their babies hiccuping in utero, and they gradually go away as children grow up.
Incidentally, many experienced nurses swear by sugar water as a cure to hiccups in infants. I already make all the kids try everything on their plates. Meat per say is not an absolutely necessary part of anyone's diet. It is important for your child to get protein and iron and other nutrients. Alternatives are fish, peanut butter, eggs and leguminous beans.