When we have a good understanding of the rules of the English language we can begin to play with them and to have fun with words. Once the rules are mastered we can then use tools such as ambiguity deliberately. In this cartoon ambiguity has been used as a tool to provide humour.
When we have a solid grasp of how to use the English language we can use it to fulfil our purposes, whether that be to make an audience laugh, to move them to tears or simply to communicate our ideas.