Bilaam's trick was that he would look at a person and curse while connecting his thoughts to the higher world and thereby his curse would take effect. We see in the gemara in various places the tremendous power of a look together with a thought. The expression "he gave me a killer look" has a lot of truth to it. Looks can kill.
"Sticks and stones will break my bones ... and so can a mean, angry look". So look at people with love.
Look at what a 14th century mekubal says!