Customs officials at Houston’s George Bush Intercontinental Airport recently discovered 30 bird’s nests smuggled into the country.

According to the U.S. Customs and Border Protection, the nests are considered a delicacy in some countries but are prohibited from entering the U.S. as they can carry diseases and viruses.

Bird’s nests are created from the solidified saliva of birds and are often used to make soup or broth.

Officials say the passenger, who was arriving from Vietnam, did not declare the items. During the passenger’s bag examination, CBP agriculture specialists found the nests concealed in a box of herbs.

“CBP’s agriculture mission requires that we safeguard America’s agricultural and natural resources,” said Port Director Charles Perez. “Our agriculture specialists recognize the importance of intercepting these types of smuggling attempts to prevent the spread of infectious diseases and harmful pests that have not been introduced into our agriculture. Seizures like this one keep that threat at bay.”

In some cultures they are considered a prized possession due to their high nutritional value and exceptional taste, according to CBP. The nests are high in calcium, iron, potassium and magnesium.

The passenger was fined $300 for failure to declare prohibited items, and the bird’s nests were seized and destroyed.