After wandering off, Peter realised that his floury hands made marks on the hall carpet, which was very popular with him! We ended up with a hall full of foot and hand prints.
Harry did all the cleaning up too! This was the sort of activity I probably never would have planned and I would have perceived a very high hassle factor but it was great and they both had fun investigating on their own. The mess was pretty well contained to the kitchen and hoovered up really easily from the carpet.