There are a lot of threads on here from tiume to time asking about repitching on yeast cakes and the like.
Here's a little info on how this works sometimes...
A couple weeks ago, I brewed an IPA. I pitched some washed slurry from a previous batch of Wyeast 1098 British Ale yeast. It was a large amount of slurry and the ferment started very quickly (lots of airlock activity within a couple hours.) Within 3 days (probably less), the kreusen had fallen and airlock activity almost stopped.
Monday, I racked that IPA, and within minutes pitched an outmeal stout onto that yeast cake. It was bubbling like mad through the blowoff tube within a half hour. 24 hours later, the kruesen had fallen and bubbling had almost completely stopped.
One caution: these fast ferments generate a lot of heat: you want to keep your primary in a cool enough place for that first day or two that an extra 6 or 7 degress won't put you over the temp range for your yeast.