Watching animals in the wild often reveals unexpected connections.
Relationships between different species normally benefit one or both of the parties: if it benefits one and harms the other it is known as a parasitic relationship, if it benefits one or both parties it is symbiotic.
The white oxpecker bird is frequently found with wildebeest and other antelopes and cattle, often catching a lift on their back. This is generally believed to be a symbiotic relationship with the birds benefitting from a regular food supply of ticks and other skin parasites, and the mammal being glad to be rid of these skin pests. In addition, the birds are generally quicker to react to danger, so acting as an early-warning alarm for the mammals.
It also seems that oxpeckers sometimes pick at the wounds of animals, keeping them open and drinking the blood of the animals. This is probably uncommon, but it could cause the relationship to be reclassified as semi-parasitic.