In Bumblebee (2018), one of the Decepticons shot the human with their gun, causing the human to explode into what looked like colorless blood:
Why does the human blood look colorless?
It's because this film has a lower age rating than the previous Transformers films, entitling young children to see it.
The MPAA rated this film as
PG-13 for sequences of sci-fi action violence
From Wikipedia:
Depictions of violence are permitted under all ratings but must be moderated for the lower ones. Violence must be kept to a minimum in G rated films and must not be intense in PG rated films. Depictions of intense violence are permitted under the PG-13 rating, but violence that is both realistic and extreme or persistent will generally require at least an R rating.
So, using "sci-fi" weapons to reduce someone to a harmless looking gloop allows the film to retain the intended PG13 rating.
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Minor point: All other live-action Transformers films have also been MPAA rating PG-13 – notovny May 3 '19 at 21:46
