That's Brooklyn's pronunciation of Smile. She'll play with Alexis and when Alexis flashes her gummy smile at her she'll shout "OOK Mae (yes, she calls me Mae)! MILES!" It's hilarous and then Brooklyn will laugh and giggle, which then Alexis will smile even bigger.
Brooklyn has also learned to tickle Alexis' feet to try and get more smiles. She'll say "tickle tickle" and giggle.