https://www.airliners.net/forum/viewtopic.php?f=3&t=1494073&...
It's not supposed to happen under normal circumstances and clearly it happened several times in a row here. Maybe some blade damage? Anyway I'm sure the investigation will turn up the cause.
I'm glad those people are ok. Though it isn't normally immediately dangerous on modern engines (e.g. it might lead to loss of thrust but not resulting in an explosion). That did happen on older engines though. I'm sure it must be scary, seeing flames and hearing bangs.
Ranting about this on the porch, the boy interrupted me and said "yeah, yeah, it's like peasants seeing a comet in the middle ages, it changes everything".
Also, this is likely a bird that got ingested.