The scene where Papa and the other Smurfs see Smurfette using the wand Gargamel gave her. The way the four are yelling her name doesn't help. Especially the way Papa yells through the glass and the fact Grouchy, Vanity and Clumsy have to stop him from climbing up the door to get to the doorknob:
Also, the scene where Smurfette sees The Naughties dying and begs Gargamel to feed them but the wizard forces her to write the formula that will turn them into real Smurfs, which she reluctantly does.
It helps the music builds the scene quite well.
Later After,Gargamel puts them into cages. Smurfette and the Naughties start crying.