Theory:

I saw a snake and ran away...
Some snakes are dangerous, they say;
But mother says that kind is good,
Explanation:
 
The poem revolves around a small incident that takes place in the speaker's garden. The speaker seems to be a child when the scenario described in the poem takes place. The poem begins by revealing the main event that led the speaker to write. He sees a snake in the garden. Generally people have their own misconceptions and understandings on reptiles and other creatures. Sometimes they are purely led by fear. They do not try to go beyond the existing beliefs and fathom into reality.
 
As soon as the speaker sees the snake, he runs away in the fear that it might cause any harm. He is led by the knowledge that he has gained from his young age. When a child is born, he does not have any beliefs or knowledge about anything. As he grows and transforms into an adult, the society feeds him its own ideals, thereby restraining him from forming his own opinions from his experiences. The poem clearly depicts this idea with the line, "Some snakes are dangerous, they say". 'They' refer to the society and their forced ideals. But at times, children can be guided in a correct way by sensible adults. In this case, the speaker's mother who corrects his distorted belief in snakes. His mother has a better exposure and with one look at the snake, she confirms that it is a harmless one. She even says that these kind of snakes in fact do good to the society.
 
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Reptiles
 
Words with difficult meaning:
 
S.No
Words
Meaning
1
ScenarioA sequence that leads to events happen
2
MisconceptionsIncorrect beliefs and understanding
3
ReptilesA class of animals that include snake, lizards, crocodiles and turtles
4
FathomUnderstand after much thought
5
IdealsOne's beliefs or standards
6
RestrainingPrevent someone from doing something
7
DistortedMisleading or misrepresented
8
ExposureA revelation by gaining maturity
9
DepictDescribe
10
SensibleUsing logic to make wise decisions
Reference:
National Council of Educational Research and Training (2007). Honeycomb. Garden Snake: Muriel L. Sonne (pp. 137-138). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.