Also, put their heads together. Discuss or plan something among ourselves (or themselves), as in Let's put our heads together and figure out what we can give him for his birthday. This idiom, alluding to combining mental forces, originated in the late 1300s as lay our heads together and acquired its current form in the second half of the 1800s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.