This is Jelly looking for mice, other small creatures or something we can't fathom, from her vantage point on the compost heap post.
She'll sit there for ages, looking intently. Sometimes a tiny twitch of her tail gives away the fact that she's thinking, but the rest of her remains completely still with the patience of a martial arts master.
This kind of self discipline is too much for the boys, whose idea of gardening is to look after the tools. From a sunny position.