Choose the correct form of the verb to fill the gaps. Use a gerund or the infinitive form of the verb.

When looking at a human face, we look left without ... it.
Scientists wanted to find out if dogs use the same trick ... human faces.
Scientists thought only humans had a left-gaze bias until they started ... at dogs.
... the ability to detect human emotions is unique to dogs.
There may be a biological advantage in ... to read people's emotions.
It makes sense for a dog ... a person when the person is smiling.