The trenches were dirty. The cold, wet and unsanitary conditions made many soldiers sick. For example, "trench foot" was a fungal disease. It rotted people’s feet off. Lice spread throughout the trenches. They spread a disease called trench fever. It caused fevers and a severe pain to the head. Rats invaded the trenches and spread disease everywhere. The brown rats were the more hated kind. They ate human remains. Some grew to be as big as cats. The mud was very thick. Some men disappeared into the mud because it was so thick.