Use "muck about" in a sentence

1. The idea of keeping company with a cartload of coffins was not Johnny's idea of fun, and the uncertainty of what they contained was beginning to muck about with his mind

2. For instance, on the planet Earth, man hadalways assumed that he was more intelligent than dolphins because he had achieved so much – the wheel, New York, wars andso on – whilst all the dolphins had ever done was muck about in the water having a good time