You dog sounds unwell. The yellow liquid is most likely bile. This is a fluid produced by the liver to aid digestion. Keep a close eye on your dog as it may have just eaten something that it shouldn't have. If you don't see an improvement in 12 hours or it gets worse contact a vet. Bare in mind that 14 is old for a dog so you may want to contact a vet sooner to be safe. Hope he/she is ok
