when using this ている form, you can omit the い and it's stil | Learn Japanese

when using this ている form, you can omit the い and it's still understandable, for example, in KonoSuba, episode 3, around minute 17:45, Kazuma says

喜んでる？ [よろこんでる？] "she's enjoying it?" when seeing his party member enjoying getting hit by cabbages