Water

Getting rabies is basically always fatal if not treated immediately. One side effect of rabies is that you won't be able to swallow. This is a slight issue as humans need to swallow water to survive. This is also what causes the typical mouth frothing look associated with rabies.

Basically, extremely painful throat spasms are triggered if you try to swallow. The virus thrives in saliva so it naturally doesn't want the host to swallow that.