Is drifting her a gerund...how do you tell if a word is a gerund?

Christian Pruett and his wife were driving on Interstate 25 on Monday morning when they noticed a sport utility vehicle next to them drifting from lane to lane.

Hi!

I am learning gerund, and hopefully I could help you out with something that I learned.

Rule one: You have to use a gerund after some verbs, such as: admit, appreciate, avoid, consider, delay, deny, endure, enjoy...

Rule two: A lot of clauses are required gerund after them, such as be fond of, can't help, can't stand, feel like, give up, keep on, insist on, put off...

And here is one of my own experience that might help you with classifying gerund:  A gerund usually stand for something that are abstract, with no real time.

e.g:  My job is teaching english (in this sentence, teaching is a gerund.)

      I am teaching my student english.(present participle)

Hope you will be able to understand them.

Still wondering...

Since the participle directly follows the noun it modifies, my teacher would have told me to use a comma.  But then again, I'm starting to notice that there is no definite way to punctuate participle phrases when they directly follow the word they modify.  Some authors will only exclude the comma to avoid ambiguity, while others seem to never use it.  I guess sometimes the use is at the authors’ digression.