Then— “Riddikulus! ” bellowed Ron, and the spider's legs vanished; it rolled over and over; Lavender Brown squealed and ran out of its way and it came to a halt at Harry's feet.
Knowing you were trying to break the record, so it was like this weird combo of like counting the rolls, wanting those rolls for you, but then also worrying about what every roll was doing to you.
When you show off, you're trying to impress somebody, trying to display your abilities, to attract attention. She showed off by doing a bunch of flips in gym class.
Show off的意思是给某人留下印象,试图显示你的能力,吸引注意力。在体操课上做了一串翻滚动作来炫耀自己。