Thanks again ajabrams.
I took a short cut in my question. ´I watch the teacher ( as in this sentence ) wouldn
t be imperative. My problem is that I am looking for something useful. I myself might say ´I watch the teacher (suggesting at what the teacher is demonstrating) but seldom ´I look at the teacher` ( the teacher in person). Because, how often do we do that?
There again, I might look at the dog or at the baby when it is they who are the object of my interest. Perhaps these teachers are particularly good looking :)