Cats sleep deeply.

Meaning: This means that cats sleep for a long time and are very relaxed when they do. It's like saying, Cats often sleep for many hours at a time and are very still when they do.

Choice of Words: Cats are animals that are known for their ability to sleep for long periods of time. Sleep means to rest or be unconscious. Deeply means to a great extent or intensity. Together, these words convey that cats sleep for a long time and are very relaxed when they do.