I remember a paper studied the effects of gender of handler on animal (mouse?) showing that male handler has more negative effects on animal (for example, causing animal anxious) compared to female technician. The animal can distinguish man and woman by their odor. This phenomenon disappears if the handler is well wrapped in gown to prevent odor from escaping it.
This paper seems published in Nature Methods. Unfortunately, I cannot find this paper now. Do you happen to know this paper? Thank you!