The opening sequence displays the activities of an avian (bird) brood parasite, which rely on other birds to raise their young. The brood parasite manipulates a host, of the same or another species, to raise its young as if it were its own, using brood mimicry, for example by having eggs (or pudgy, weird babies) that resemble the host's. This behavior relieves the parents from the investment of rearing young. Some bird species mitigate the risk of egg loss by distributing eggs among a number of hosts.
The exteriors for house number 9 were a set that was built inside of a warehouse.
The scene at the school was one of the few scenes shot on location.
Poots offered Eisenberg a male lead role, and Eisenberg accepted the offer. Poots said, "I thought Jesse would be awesome to play Tom. Luckily, he was available and up for it, which I'll say is super cool. On the page, it was certainly a female-centric film in the sense that Gemma had been written as "the lead" or what have you. It's quite rare for a male actor to say, "Yeah, I'll play the other part...." So, it was really, really cool and supportive that he was up for it. That's how it came about, and we got to work not long after that. He's amazing that way; he's so loyal and cool."
Martin's car has Waterford plates, Gemma and Tom's has Kilkenny, so probably shot in south east counties of Ireland.