Answer:
Hi!
The answer to your question would be that your dog went through a "spontaneous recovery".
Step-by-step explanation:
To understand why this is the answer, we first need to know what spontaneous recovery means. The term "spontaneous recovery" refers to the re-emergence of a previously extinguished conditioned response after a delay. In this case, we can see that Milo was trainned to stop salivating with the sound of the bell. The conditioned response here would be Milo not salivating, and the re-emergene of the previously extinguished condition would be him salivating again the next morning.