A "sensorial explorer" is how Montessori would define an infant from birth-and possibly before. What is the child exploring? Their environment. The number one environment for an infant is their home, and you can provide many opportunities to assist your baby in this work. The activity Dotty and I did above is pretty self explanatory from the photos. I always pour water for her to try to catch in the bath while saying "water". It is so basic and foundational, after all it is with that action that Anne Sullivan was able to unlock learning for Helen Keller.
We did this activity in the kitchen because that is where she sees these materials used daily. Children love getting their hands on the tools they have seen you work with.
Some helpful hints when doing this activity: about 2 inches of water is enough/ you'll need to sit with one hand on the dishpan to prevent it from tipping/give baby the names of each tool-"whisk" "spoon" etc..