pieskiem

In a sentence

• Mój sąsiad chodzi na spacer z pieskiem każdego ranka.

  My neighbor takes his dog for a walk every morning.

  In this sentence, 'pieskiem' is used as an instrumental singular form of 'piesek' (a diminutive form of 'pies', meaning 'dog'). It shows possession and indicates an endearing tone.

• Gdy zobaczyłem tego pieska na ulicy, poczułem smutek i współczucie.

  When I saw this little dog on the street, I felt sadness and compassion.

  Here, 'pieska' refers to 'piesek' in its singular accusative form, used to express the object of the emotion and observation.

• Dzieci bawiły się z pieskiem w ogródku.

  The children played with the small dog in the garden.

  The word 'pieskiem' in this context is a singular instrumental form again, indicating the entity with which the children are playing, with a diminutive and affectionate connotation.