Just got the MN developmental email for dd2 who is 9 months tomorrow which mentioned the brick test - handing them a third when they already have one in each hand.
So I thought I'd try it on dd2. Handed her 2 bricks then proffered the 3rd - she didn't hesitate just opened her mouth & bit the brick then sat there pleased as punch with her 3 bricks - not the calmly considered approach suggested in the email! I did already know I hasd a dd2 who knows what she wants!
Try it on your 9 month old & let me know what happens!!