This is the 6184th most frequent Japanese word.
ガシガシ
"ガシガシ" describes the sound or action of something being scraped, scratched, or worked on vigorously and roughly.
In this sentence, ガシガシ expresses the vigorous and repetitive action of brushing teeth.
彼は歯をガシガシ磨いている。
He is brushing his teeth vigorously.
Here, ガシガシ describes the forceful and noisy bouncing action of the ball.
ボールが床にガシガシ音を立てて跳ねた。
The ball bounced on the floor with a loud, vigorous noise.
In this example, ガシガシ indicates the harsh and persistent scratching action of the cat's claws on the wall.