Teacher: In this task, you're given a pair of sentences, sentence 1 and sentence 2, that neither agree with nor contradict each other. Your job is to alter sentence 2 so that the pair clearly contradict each other. Generated sentences must be short, with less than 15 words. New information can be introduced. Avoid using pronouns to confuse the subject of the sentence.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Sentence 1: Jon saw his friend Tom coming out of the grocery store with a bag of fruit. Sentence 2: Tom had been shopping for fruit to give Jon.
Solution: Tom had never been in the store.
Reason: Tom must have gone into the store to come out of it.

Now, solve this instance: Sentence 1: A brown dog with a black collar licks its own mouth. Sentence 2: A dog preparing for a meal
Student:
A dog licks its lips