We've all heard the story of Three Little Pigs. The third pig foiled the hyperventilating wolf by building his house out of bricks, rather than with straw or sticks as his brothers had done. Less commonly known is that the pig later improved his home's safety profile by installing convex  security mirrors at key points along the driveway. Well, why not? In the current issue of Animal Behaviour, researchers present evidence that domestic pigs can quickly learn how mirrors work and will use their understanding of reflected images to scope out their surroundings and find their food. The researchers cannot yet say whether the animals realize that the eyes in the mirror are their own, or whether pigs might rank with apes, dolphins and other species that have passed the famed "mirror self-recognition test" thought to be a marker of self-awareness and advanced intelligence. The finding is just one in a series of recent discoveries from the nascent  study of pig cognition . Other researchers have found that pigs are brilliant at remembering where food stores are cached and how big each stash is   to the rest. They've shown that Pig A can almost instantly learn to follow Pig B when the second pig shows signs of knowing where good food is stored, and that Pig B will try to deceive the pursuing pig and throw it off the trail so that Pig B can hog its food in peace.  They've found that pigs are among the quickest of animals to learn a new routine, and pigs can do circus worth of tricks: jump hoops, bow and stand, spin and make word like sounds on command, roll out rugs, herd sheep, close and open cages, play videogames with joysticks, and more. For better or worse, pigs are also slow to forget. "They can learn something on the first try, but then it's difficult for them to unlearn it," said Suzanne Held of the University of Bristol. "They may get scared once and then have trouble getting over it." Pigs can play all the tricks, except   _  .
herd sheep play video games with joysticks sing and dance bow and stand
Question: We've all heard the story of Three Little Pigs. The third pig foiled the hyperventilating wolf by building his house out of bricks, rather than with straw or sticks as his brothers had done. Less commonly known is that the pig later improved his home's safety profile by installing convex  security mirrors at key points along the driveway. Well, why not? In the current issue of Animal Behaviour, researchers present evidence that domestic pigs can quickly learn how mirrors work and will use their understanding of reflected images to scope out their surroundings and find their food. The researchers cannot yet say whether the animals realize that the eyes in the mirror are their own, or whether pigs might rank with apes, dolphins and other species that have passed the famed "mirror self-recognition test" thought to be a marker of self-awareness and advanced intelligence. The finding is just one in a series of recent discoveries from the nascent  study of pig cognition . Other researchers have found that pigs are brilliant at remembering where food stores are cached and how big each stash is   to the rest. They've shown that Pig A can almost instantly learn to follow Pig B when the second pig shows signs of knowing where good food is stored, and that Pig B will try to deceive the pursuing pig and throw it off the trail so that Pig B can hog its food in peace.  They've found that pigs are among the quickest of animals to learn a new routine, and pigs can do circus worth of tricks: jump hoops, bow and stand, spin and make word like sounds on command, roll out rugs, herd sheep, close and open cages, play videogames with joysticks, and more. For better or worse, pigs are also slow to forget. "They can learn something on the first try, but then it's difficult for them to unlearn it," said Suzanne Held of the University of Bristol. "They may get scared once and then have trouble getting over it." Pigs can play all the tricks, except   _  .
A. herd sheep
B. play video games with joysticks
C. sing and dance
D. bow and stand
Answer: