This early 70's giallo by Umberto Lenzi is certainly among the best in his filmography and also in the whole genre. Personally I think Lenzi's best films are the funny cartoon-turned-film Kriminal, the stylish giallo Seven Blood-Stained Orchids, the explosive Napoli violenta and this. In the eighties he did plenty of film trash in form of Eaten Alive, Hitcher in the Dark or Black Demons, all of which are ripping something off and/or very dull and slow moving. Knife of Ice came when the giallo boom was at its hottest and the result is convincing.
　　Technically the film is superb, containing great cinematography in the beginning when we learn about the main character's trauma towards trains. From this point on, Lenzi shows us his ability to benefit the widescreen and, for example, the bicycle ride near the forest is genuinely beautiful! This scene also shows Lenzi's ability to build suspense, very slowly but meaningfully. After all, there aren't so many murders in the whole film, only the suspense circulating around the murderer's identity.
　　One suspect is a devil worshipper which brings new aspects to the mystery. Since the final scene takes place in a church, one can wonder if Lenzi wanted to comment on something, maybe the hypocritical morale of church and superstition. The main character (Carrol Baker) is mute which demands a lot from her face and eyes. The actress works very well, giving us a believable performance circulating around the emotions of fear and mental pain. The other actors are good, too. The finally, however, may not give too positive a sight about female sex since they all are expressed rather negatively in the film, one way or another. Still this is easily among the most noteworthy in the genre, not as bloody as the Argento films, for example, but equally suspenseful and visually also interesting.