It is worth noting that Seamus believes the shrieking from the golden egg is that of a banshee, which is the form his boggart took during Defense Against the Dark Arts, the previous year. Neville believes that the shrieks from the golden egg are those of someone being tortured by the Cruciatus Curse, which George reminds him is illegal. (Neville witnesses the Cruciatus Curse being performed on a spider by fake Professor Moody in his first Defense Against the Dark Arts lesson of the year, and given his knowledge of his parents' torture under that curse, it is likely still fresh in his mind at this time.)
It is worth noting that Seamus believes the shrieking from the golden egg is that of a banshee, which is the form his boggart took during Defense Against the Dark Arts, the previous year. Neville believes that the shrieks from the golden egg are those of someone being tortured by the Cruciatus Curse, which George reminds him is illegal. (Neville witnesses the Cruciatus Curse being performed on a spider by fake Professor Moody in his first Defense Against the Dark Arts lesson of the year, and given his knowledge of his parents' torture under that curse, it is likely still fresh in his mind at this time.)
--AK