Good gracious ... you are in for a world of trouble and misery if you don’t know that there is a major difference between A hydra and The hydra!
If your mom sends you out to get A hydra and you bring back The hydra you are going to be in the worst trouble of your life!
The last person to go out looking for The hydra was Herakles and if the goddess Athene hadn’t been there to protect him, he might not have survived the encounter.
The last person to go out looking for A hydra had a pleasant afternoon and came back thoroughly refreshed.
As you can easily perceive, there is a tremendous difference between A hydra and The hydra.
I hope you’ve learned something here ... unless you happen to have Athene and Herakles with you, stay away from The hydra.