The technique I was speaking of is known as Grimm's Law.
From another answer I posted a while back:
The main difference between the Germanic languages and the Latin (and Celtic) languages is Grimm's Law, which describes a set of sound changes that map Germanic words to their Latin and Celtic cognates. The Germanic sounds were shifted from their Proto-Centum or Proto-Indo-European forms, while the Latin and Celtic sounds either did not change or were changed in some other way (out of scope of this answer).
English tooth corresponds to Spanish diente.
English three corresponds to French trois.
German hund and English hound correspond to Classical Latin canis.
English fish corresponds to Spanish pez.
English foot corresponds to French pied
See my answer linked above for more examples (and a better explanation of them), and also see the original article I linked to for an in-depth look at the law.
In your case, you should note that additional sound shifts have occurred in French. For example, the word for "dog" is chien, which has undergone a sound shift from Latin hard-c to a soft "sh". Similarly, French "chaud" corresponds to English "hot" - the French "ch" comes from the Latin "c" (with the "d" remaining unchanged), and the English "h" and "t" come through Grimm's Law.