Theory:

     I could see the corner, in a haze. I was starting to whoop with glee, but the whoop froze on my lips. There, right in the middle of the road, stood alone cow! I jammed on the brakes and the cycle stopped abruptly, but I could not stop the momentum of my own body. I flew over the handlebars and landed smack on the back of the unfortunate animal. The cow, startled by this sudden attack, reared up and started running. I clung to her for dear life, as she charged up the road and round the corner.
Explanation:
 
The siblings have a race between them, which the author is determined to win. She needs to win this race as she had never won a race with her brother and wants to prove him wrong. As she picks up speed, she notices that the corner her brother had fixed as the winning destination was looming near. She could not believe her eyes as her success lay only a few meters apart. She started shouting in happiness, but her cry of joy froze on her lips all of a sudden as she sees an obstacle between herself and the destination. It was a cow which stood alone in the middle of the road, unaware of the racing bike that was heading towards it.
 
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The cow stands in the middle of the road
 
The author steps on the breaks of the cycle all of sudden due to her instincts. But just like the cause of any other accident, she had to react on her whim as she had totally not expected to come across the cow. She did not have time to plan her next move, which made her apply the brakes all of a sudden. She could not control her body movements because she was riding the cycle at high speed to race along with her brother. She falls in a forward direction, because when she applies the brake, both the cycle and the upper part of the body are in motion. Thus it is difficult to gain control over one's body when one is racing at a maximum speed. She therefore flies away from her seat, leaving the clutches of her handlebar, and lands on the back of the cow.
 
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The girl flies from the cycle, losing balance
 
The poor cow who was not expecting this sudden attack, gets startled and starts running. This is because of the shock and confusion caused due to the sudden movement in his body. The cow thinks that there is danger approaching it and therefore runs for its dear life. It is not aware of what is happening around, and acts on an impulse just like the author. The author clings on to her dear life as she sits on top of the cow. The cow races across the road as it is fully charged up due to the commotion. It had been disturbed and awakened from its routine lethargic mood. It is funnily portrayed as to how the author wanted to win the race with her brother but ends up going on a race with the cow. The cow takes her round the same corner that her brother had fixed as destination. She had not expected to finish off the race and reach the winning point sitting on top of a cow, instead of a cycle.
 
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The cow is startled by the sudden movement
 
Words with difficult meaning:
 
S.No
Words
Meaning
1
HazeNot clear
2
WhoopAn exclamation, a cry of joy
3
GleeHappiness
4
JammedApply pressure
5
AbruptAll of a sudden
6
MomentumThe ability of the body to maintain speed
7
SmackA sharp blow
8
RearedTo rise up
9
ClingTo hold on
10
LoomTo rise and show a bigger picture
11
InstinctA natural reaction, without much thinking
12
WhimActing without reasoning or logic
13
LethargicSlow and lazy
Reference:
State Council of Educational Research and Training (2019). Term-3 English Standard-6. That Sunday Morning (pp 91-105). Published by the Tamil Nadu Textbook and Educational Services Corporation.