Discuss the difference in meaning of each of the following three almost identical sentences, which all have the same grammatical structure

Discuss the difference in meaning of each of the following three almost identical
sentences, which all have the same grammatical structure. (These are due to Keith Devlin.)
1. She saw him in the park with a dog.
2. She saw him in the park with a fountain.
3. She saw him in the park with a telescope.