Jimmy's family was on their way to a beach vacation.
As they drove along, his parents and twin brother Jason were talking excitedly.
"I'm going to walk on the beach every morning," Mom said.
"I'm going fishing," Dad said.
"Can we go to the amusement park?" Jason asked.
"There's a new roller coaster—Motion Monster."
Jimmy stayed quiet.
"What's wrong, Jimmy?" Mom asked.
He shrugged. "Nothing."
"I know what's wrong!" Jason grinned.
"This is a long car ride.
He's worried he's going to throw up!"
"I brought some stuff, in case you do feel carsick."
Mom held up a bag.
"I've got peppermint gum, ginger candy, wristbands, and even some medicine.
One of these treatments might help."
Jimmy sighed. "Why do I get carsick anyway?"
"It's called motion sickness," Mom said.
"It comes from your ears and your eyes having a disagreement."
"Kind of like . . ." Jimmy looked at Jason. "Twins disagreeing?"
"Not exactly," Mom said.
"Motion sickness occurs when one sense detects motion, but another one does not.
For example, if you're reading in the car, your eyes think you're staying still.
Meanwhile your ears detect motion, and the two senses clash."
"So your brain gets different messages," Dad added.
"And you start to sweat or feel sick to your stomach."
"I never get carsick," Jason bragged.
"Doctors aren't sure why some people get motion sickness and others do not," Mom said.
"But it's very common, especially among kids."
"Grandma gets motion sickness on airplanes," Dad said.
"My friend Shin gets seasick on boats.
He eats ginger before he goes sailing—that's what Chinese fishermen have done for centuries.
It calms your stomach.
Another trick is to stare at the horizon when you're seasick."
"Uh-oh . . ." Jimmy could see that their car was approaching a curvy road.
"Here." Mom handed him the gum.
"The doctor said peppermint is good for stomachaches.
Roll down your window for fresh air.
Don't read or look at a screen."
Jimmy followed his mom's advice.
As the car drove along the road, he chewed gum and closed his eyes.
"How's it going?" Mom asked.
He took a deep breath. "Good! I feel fine!"
The week at the beach flew by.
One cloudy day the family went to the amusement park.
"Whoa, check it out!" Jason pointed to Motion Monster.
It was an enormous roller coaster with steep hills and huge loops. "Let's go!"
The twins raced over to the ride and hopped into the first car.
Minutes later they began going up the first slope.
"Ahh!" Jason screamed as they flew downward.
Jimmy threw his arms up. "Whee! This is awesome!"
But when he looked over at his twin, he saw Jason clutching his stomach.
"What's wrong?" Jimmy asked. But he already knew the answer.
Jason had motion sickness!