Humans and animals share common behaviors, like smiling.

Dolphins smile by opening their mouths when they play, according to a study by French and Italian researchers at the Zoomarine Rome and Planète Sauvage in western France, respectively, as reported by CNN.

The researchers observed that dolphins “smile” when they see their kind during playtime (leaping, breaching and flipping), but do not open their mouths when engaged in aggressive interactions or more relaxing activities, like parallel or upside-down swimming, CNN reports.

Other wild animals exhibit more humanlike behaviors, which the animal rights group Nonhuman Rights Project (NRP) highlighted in a lawsuit it recently filed with the Colorado Supreme Court against the Cheyenne Mountain Zoo (CMZ) in Colorado Springs.

NRP lawyer Jake Davis contended during oral arguments that wild animals are intelligent, sensitive, friendly and capable, and therefore deserve personhood and autonomy.

Former state attorney general John Suthers, representing CMZ, rejected NRP’s petition to have Missy, Kimba, Lucky, LouLou and Jambo released and transferred to an elephant sanctuary.

Suthers invoked CMZ’s statutory authority to hold the five elephants and insisted that the zoo had not violated any laws.

The state Supreme Court’s justices will decide the case next year, according to CPR News.