Respuesta :
the dilation or the widening of the pupils. The dilation of the pupils is usually an involuntary body movement that would occur if one is excited or aroused by something, which is quite normal for most people to exhibit if they are in love and looking at the person they love.
I believe the answer is: dilation of the pupils
Our pupils would automatically dilated whenever we feel a certain level of excitement. During interaction between two different people, this excitement could be interpreted as sexual attraction. This is why Paul's wife could detect paul's interest. (especially if they are currently conducting a physical contact)