There was no pack, no coal-oil cans of water; only the halter and lead rope, that dangled and caught on brush and impeded William's limping progress.

I suppose even miserable mules like company, for William permitted Casey to walk up and take him by the halter rope.

William had a badly skinned knee which gave him the limp, and his right ear was broken close to his head so that the structure which had been his pride dropped over his eye like a wet sunbonnet.
Casey swore a little and started back along William's tracks to find the water cans.

He followed a winding, purposeless trail that never showed the track of burros, and after an hour or so he came upon the pack and the cans.

Evidently the water supply had suffered in the wind, for only four cans were with the blankets and pack saddle.
William had felt his pack slipping, Casey surmised, and had proceeded to divest himself of the incumbrance in the manner best known to mules.
Having kicked himself out of it, he had undoubtedly discovered a leaking can--supposing the cans had escaped thus far--and had battered them with his heels until they were all leaking copiously.