Often, before I do something fun to Annika (18 months), like drop her on a bed or couch, I count down...1, 2, 3. This is tremendous fun and leads to the inevitable giggles and smiles. She's taken to counting down with me, although she only knows one number: 2.
The other day she was on my bed and threw herself back with a bounce. She then sat up and announced, "I do two, two!" It was really cute.