Play NYT Connections Puzzle #321 Mon, Apr 15

Find groups of four related words Need hints?

Solve NYT Connections puzzle #321 - Group 16 words into 4 categories: AD-LIB, FREESTYLE, IMPROV, MAKE UP, BABBLE, COO, CRAWL, NURSE, COSMETIC, EXTERNAL, SHALLOW, SURFACE, BUTTERFLY, DOMINO, PLACEBO, SIDE.