10/31/2011 02:50 pm ET Updated Dec 31, 2011

Neil Patrick Harris On Katie Holmes: 'Really Smart'

How I Met Your Mother has had their fair share of big names on the show (Britney Spears, Jennifer Lopez, John Lithgow...to name a few). And tonight they're adding Katie Holmes to the list when she guest stars as the legendary Slutty Pumpkin from Ted's Halloween past.

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