Why did Katrina slap Imran Khan???

‘Mere Brother Ki Dulhan’ stars Imran Khan and Katrina Kaif, in the lead. The shooting is already on and during one of the shoots, Imran was slapped sixteen times instead of once, by the gorgeous lass. The most interesting part was Imran himself insisted that Katrina should slap him more, infact 16 times.
Imran, like is mamu Aamir is a perfectionist and so in order to make the scene look real, he insisted on Kat slapping him till the shot was perfect.
Even though this request of Imran came as a surprise to Katrina, she is not very proud of slapping him so many times but she definitely is happy about the slaps being completely real and authentic.