Paired up in the right setting，dogs and horses can have their fair share of fun-at times even playing together and mimicking（模仿）each other's facial expressions，new research suggests.These findings，published in the journal Behavioural Processes，mark the first example of so-called rapid facial mimicry occurring between play partners of different species，and indicate the existence of a universal language of play.Though the purpose behind play remains unclear，scientists believe the behavior arises to help animals improve hunting and social skills，relieve stress or develop relationship with each other，study author Elisabetta Palagi says，an animal behaviorist at the University of Pisa in Italy.
 Learning more about the contexts in which different animals play around-especially across branches of the tree of life-could tell researchers a lot about play's origins and evolution .But apart from a handful of studies featuring humans and their pets，scientists haven't had many chances to analyze examples of interspecies（種間）play.
 In 2018，when someone sent Palagi a YouTube video featuring a dog and a horse playing together，she took the chance to research furjye.air.The two species，she noted early on，were especially good research objects of interspecies friendship，because they had both been shown to recognize facial expressions in other animals.
 Putting together a team of research students，Palagi began to collect and analyze hundreds of other videos with dogs and horses partnering in play.Only 20 videos ended up meeting the team's requirements：showing animals freely playing on their own，without human interference（干擾），for at least 30 seconds.
 Several common themes quickly arose.When playing，dogs and horses often mirrored each other's moves，jumping and pushing at each other.They also rolled on their backs and showed their throats and stomachs-a strong sign that they were at ease and even communicating their friendly intentions .Despite millions of years of evolution between them，the two species had found common ground for the only purpose of fun，said Palagi.
 The two animals also frequently copied each other's facial expressions，both using the relaxed，open mouths-behavior that had never been noted between a pair of animals of different species.Horses and dogs may look and behave in extremely different ways，says Barbara Smuts，a behavioral ecologist at the University of Michigan who wasn't involved in the study.But fun is perhaps a language that doesn't need to be taught.Two very dissimilar animals，Smuts says，can still discuss how to play in a way that's comfortable for both.

（1）What do scientists find about dogs and horses？

A

A

A．They share similar facial expressions.
B．They can build up a lasting relationship.
C．They often share hunting and social skills.
D．They have a special way to communicate.
（2）How did Elisabetta Palagi study dogs and horses further？

C

C

A．By playing with dogs and horses together.
B．By pairing up dogs and horses in a setting.
C．By watching videos showing their play scene.
D．By recording their play for 30 seconds every day.
（3）What does the underlined part "at ease" in Paragraph 5 most probably mean？

A

A

A．Feeling relaxed.
B．Looking similar.
C．Getting smart.
D．Turning sociable.
（4）What is the significance of the study？

B

B

A．It can help humans get along with animals.
B．It studies interspecies play for the first time.
C．It explains animals' way of communicating.
D．It analyzes animals' facial expressions in detail.