Q:  What do you call a scared cow?
A:  A milk shake!

Explanation:  When people get scared, frightened, they sometimes shake because of the fear they feel.  A milkshake is a drink that mixes (or shakes) together ice cream and milk (sometimes with fruit or chocolate or …).  So, if you shake a cow (which would be really hard to do!) you could get a milk-shake.  Or if the cow gets scared it could shake itself and the milk that is inside it thereby making a milkshake.  Crazy!  It could never happen!  That’s why it’s funny!