The speaker remembers a cold, yellow morning when they walked through a wood beside a brook and met a group of heifers. The animals are curious but cautious, and the speaker is careful not to crowd them. When the speaker stops on a flat gray stone, the heifers bolt, and the speaker worries that they have caused some harm.
Then one Jersey heifer comes back alone. She and the speaker stand still, each watching the other, and she tilts her head as if asking a question. Her eyes are "unafraid." After a moment she kicks up her heels and dashes off, playful rather than frightened.
The mood is gentle, hushed, and a little wistful. The repeated lines, like the heifers startling or the leaves trembling, work like echoes, as though the speaker is turning the memory over. The final words, "long ago," suggest how precious this small moment of trust has remained.