Your tamagotchi is celebrating Easter! Tamagotchis do this from late March into early April is they are adults. The thing is an egg, and the black thing is a baby! (On the versions besides V4, your tama watches the Easter Bunny )
I've never had it, but I've read about 112 topics about it in the last month. In the month of April (and probably late March), tamagotchi starts watching an egg that hatches as an Easter animation. Sorta like in August or something Entama watches these weird things that's supposed to be a wind chime. Or in January V4s watch Snowmen.