Theory:

He wore a question mark for tail,
An overcoat of gray,
He sat up straight to eat a nut.
He liked to tease and play,
And if we ran around his tree,
He went the other way.
Explanation:
 
The Squirrel is a small poem written by Mildred Bowers Armstrong.
 
squirrel-493790_1920.jpg
A red squirrel
 
A squirrel is a small playful rodent that usually lives in trees. Here the poet is describing the squirrel's physical appearance and its activities.
  
The poet refers to the squirrel as "he". The squirrel has a tail in the shape of a question mark.
 
question-1243504_1280.png
Squirrel's tail resembles a question mark
 
The colour of his body is gray. The poet refers to it as an overcoat as it has thick fur. They are generally very fond of nuts and fruits. Here, she says the squirrel has sat up straight (with his back straight) to eat his nut.
 
grey-squirrel-1451040_1920.jpg
The squirrel had gray fur and was fond of nuts
 
Squirrels are very playful and active animals. If we try to go near, he runs away as fast as he can. He likes to tease and play with us. He'll try to play by making us come near him, but if we go near himhe will go the other way.
 
squirrel-2478517_1920.jpg
The squirrel runs the other way
 
Note the rhyming words in the poem at the end of alternate sentences: gray - play - way.
Reference:
National Council of Educational Research and Training (2007). The Squirrel - Mildred Bowers Armstrong (pp. 17). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.