{"fact":"In a two-step problem-solving task, rooks spontaneously used a large stone to obtain a smaller stone, then used the smaller stone to access a worm, all on the first try.","context":"All four subjects spontaneously solved the task on the first trial, inserting the large stone into the tube with the small stone, and then inserted the small stone into the narrow-aperture tube to release the worm.","source":"Nathan J. Emery, Insight, imagination and invention: Tool understanding in a non-tool-using corvid, 10.1017/cbo9780511894800.006","index":451}