"Lobster Crawl" -- Ted fills in as Marvin’s Nanny, leading Marshall (Jason Segel, right) and Lily (Alyson Hannigan, left) to realize that Ted is using baby Marvin to replace his other baby…the GNB building, on HOW I MET YOUR MOTHER, Monday, Dec. 3 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Carin Baer/Fox © 2012 Fox Television. All Rights Reserved.

"Lobster Crawl" -- Robin (Cobie Smulders, right) is determined to get Barney (Neil Patrick Harris, left) back no matter what it takes, on HOW I MET YOUR MOTHER, Monday, Dec. 3 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Carin Baer/Fox © 2012 Fox Television. All Rights Reserved.

"Lobster Crawl" -- Robin is determined to get Barney (Neil Patrick Harris) back no matter what it takes, on HOW I MET YOUR MOTHER, Monday, Dec. 3 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Carin Baer/Fox © 2012 Fox Television. All Rights Reserved.

"Lobster Crawl" -- Robin (Cobie Smulders, right) is determined to get Barney (Neil Patrick Harris, left) back no matter what it takes, on HOW I MET YOUR MOTHER, Monday, Dec. 3 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Carin Baer/Fox © 2012 Fox Television. All Rights Reserved.

"Lobster Crawl" -- Robin (Cobie Smulders, right) is determined to get Barney (Neil Patrick Harris, left) back no matter what it takes, on HOW I MET YOUR MOTHER, Monday, Dec. 3 (8:00-8:30 PM, ET/PT) on the CBS Television Network. Photo: Carin Baer/Fox © 2012 Fox Television. All Rights Reserved.