In just three short lines, the speaker admits something quietly wistful: they often wish they could live their dog's life. The word "often" matters. This isn't a passing joke but a feeling that keeps coming back.
The poem never says why, so we're left to fill in the gaps. Judging by what we know about dogs, the speaker may be picturing a life without worry: sleeping when tired, being thrilled by a walk, loving people without overthinking it. If so, the wish suggests that the speaker's own life feels heavier or more complicated by comparison. There's also a hint of affection, since the speaker clearly watches the dog closely and sees something enviable there.
The mood is gentle, a little sad, and a little humorous all at once. The brevity helps. Like the dog's life it admires, the poem is plain and uncluttered, and it leaves a lingering question about what we might be missing.