Personification

The tree snarled.

What is the non-human object in this comparison?

A tree.

What human characteristics are being given to that object?

The tree is angry. It is snarling.

What is the effect of this use of personification?

There is more description than simply saying that the tree looks angry, or that it looks like it has a face. By saying that the tree is snarling, the reader begins to picture an angry tree. This may then attribute to the mood of the writing, casting a gloomy or scary feeling on the writing.

The idea flew from her mind.

 
What is the non-human object in this comparison?

An idea.

What human characteristics are being given to that object?

It flew. The idea was able to move.

What is the effect of this use of personification?

Giving an idea the ability to move, or fly, makes it seem like something that can't be grasped. The reader begins to see how fleeting and temporary something like an idea can be.
 
 

Time slipped away from me. 

What is the non-human object in this comparison?

Time.

What human characteristics are being given to that object?

It is able to move. It slipped.

What is the effect of this use of personification?

While time can not literally slip, most people have experienced a moment when time seemed to just get away from them. Time isn't going anywhere; however, since there is no way to hold onto the concept of time, a person may feel powerless and unable to hold onto a moment.