If your pet is showing signs of illness and you need to take it to the vet, it would be very useful to film the symptoms using your phone. It is hard to describe abnormalities to the vet, but a film would make it clear to the vet what was happening. For example, a funny cough, strange behavior or unusual sound can be recorded on your phone making it easier for your vet to make an accurate diagnosis of the problem. When clients explain funny noises, fitting, collapse, stiffness etc it is sometimes difficult for me as a vet to fully appreciate what they really mean. Film it and show the vet at the consultation.
Some mobile phone cameras have a slow motion feature. It would be very useful to film a lame pet in slow motion. This would greatly aid the vet in determining the source of the lameness.
Simple photographs of diarrhea, sick or unusual urine can help your vet a great deal. Often describing these things is hard.