Why did Lavender Brown giggle at the Yule Ball restrictions?

Question

Lavender and Parvati obviously find McGonagall's description of the Yule Ball amusing.

"The Yule Ball is approaching - a traditional part of the Triwizard Tournament and an opportunity for us to socialise with our foreign guests. Now, the ball will be open only to fourth-years and above - although you may invite a younger student if you wish -"
Lavender Brown let out a shrill giggle. Parvati Patil nudged her hard in the ribs, her face working furiously as she, too, fought not to giggle. They both looked around at Harry.
_{(Goblet of Fire, Chapter 22, The Unexpected Task)}

Specifically, they laugh at Harry and the requirement that only older students are allowed to go. What's the joke? I don't understand why they would both look round at Harry at that moment.

Answer 1

Probably because one of them wanted to go with Harry.

Parvati and Lavender looked at Harry while McGonagall was talking about who could attend the ball. This would suggest that they were interesting in going with Harry.

Indeed, Parvati does later go to the Yule Ball with Harry, and (initially) is rather enthusiastic about it.

“Wait here,” he said to Ron, and he stood up, walked straight up to Parvati, and said, “Parvati? Will you go to the ball with me?”

Parvati went into a fit of giggles. Harry waited for them to subside, his fingers crossed in the pocket of his robes. “Yes, all right then,” she said finally, blushing furiously.

—Harry Potter and the Goblet of Fire

Lavender, Parvati, and Harry are all in the same year, so the statement that "you may invite a younger student if you wish" is probably not relevant. It might seem that it must be, since Parvati and Lavender start laughing as soon as McGonagall mentions inviting younger students, but keep in mind that this is the same sentence in which she announced the Yule Ball in the first place.

One other possibility is that Parvati, Lavender, or both, could be older than Harry by a few months. This note indicates that Parvati was older than Harry, but it is based on the supposition that Padma was taking Potions in HBP, which, based on a text search, does not seem guaranteed. In any case, they could have been appreciably older than Harry, which might explain their laughing at that exact time. On the other hand, they could have been a few months younger, which might also provide a reason. It doesn't seem likely that Parvati and Lavender would consider someone in the same year "a younger student," but it is possible.

Answer 2

I didn't read the joke as relating to the "you may invite a younger student if you wish" specifically when I read the book.

One of the big themes in that particular part is how oblivious Harry is to the social protocols, and awkward around girls, etc. A main tradition of the Triwizard Tournament is the "lead dance" with the champions and their partners, of which Harry is one.

Harry doesn't even realise this is a thing for a while (iirc, McGonagall is basically like "You better actually ask someone or else you'll embarrass us" [paraphrase]), but other people are far more knowledgable, and these girls in particular are shown to be exceptionally socially aware. The picture of him dancing with a girl is a joke in and of itself.

As The Dark Lord mentioned in a comment, it could also be an allusion to Harry-Ginny. But unless there's Word of God evidence for it (which I haven't seen), I don't think the books alone contain evidence that that is likely.

Answer 3

Perhaps, like Hermione, they saw that Harry (subconsciously for now) liked Ginny and they expected him to ask her. The two of them were also Hermione's closest dormitory friends and were likely to have had a slight joke with Hermione and each other about Harry and Ginny's relationship. They probably giggled thinking about Harry asking Ginny to the ball, not to mention the way they sometimes were a bit nervous around each other.

Answer 4

Considering the very convenient line of 4th years and above, it is likely the ball would only have been open to the years that could participate in the tournament. Due to Harry, that boundary has shifted downwards rather dramatically, making it a rather giggle-worthy ammending of the rules.

Answer 5

I actually thought that perhaps they had had a divination session where Trelawney had "predicted" for the girls that one of them would go to the yule ball with Harry. Don't know why but that's what popped into my head when I first read it.