I agree with many points made by fellow commentators. This was one of director Philippe Mora's best efforts: atmospheric, grisly and featuring an extraordinary cast of slumming actors. The makeup transformation effects by the Burman studio are quite well done. BUT...
Why isn't this called The BUG Within? This poor kid doesn't turn into a beast - he turns into a gosh-darn GIANT CICADA! WTF? Where did that come from? There's no explanation in the script, and according to those who've read the source novel, it's completely different from the original story. I remember seeing this at a United Artists screening in Los Angeles back in 1982. My buddy Mike and I were big horror fans, and after the screening let out we kept asking each other, "But why did he turn into a BUG?" Neither of us could come up with an answer then and obviously, even after all these years and with all these discussions on IMDb, no one else has either.
Screenwriter Tom Holland probably could however. Certainly he's proved himself a talent in the horror genre, with his terrific script for the first Psycho sequel and subsequent work on the first Child's Play and his directorial debut, Fright Night.
Philippe Mora has had a more checkered career. A strong visual stylist, he's struggled with poor choice of material such as the infamous sequel Howling III: The Marsupials.
The Bug - sorry, BEAST Within is definitely worth a look for horror buffs, but when you watch the big transformation scene two-thirds of the way through, I guarantee you'll be scratching your head afterwards. The makeup FX are pretty cool though.
