To sneeze is to draw out air suddenly, making a loud noise. For example, when someone has a cold. It can also be used as a noun as the act or the sound of sneezing.
To sniff is to draw in air through the nose, making a slight noise. For example, you sniff the wonderful smell from the kitchen. It can also be a noun, referring to the act or the sound of sniffing.
The police dogs that help to hunt for drugs and explosives are called 'sniffer dogs'.
To sniff at someone is a phrasal verb. It means to dislike someone. The phrase 'not to be sniffed at' is common. It means that something is not to be regarded as unimportant.
Example: Think about it. Such a good job offer is not to be sniffed at.
To sniff out means to find or detect by the sense of smell.
