When adding the s ending to a verb in the third person singular in English, there may be some spelling changes:
• Add es to a verb which ends in a whistling sound ( s,sh,ch,x,z,o)
I wash – Suzy washes her car once a week.
I do – Suzy does the dishes every Wednesday.
• In verbs that end with y preceded by a consonant, drop the y, replace it with i and add es. However, If the y is preceded by a vowel (a,e,i,o,u) just add s.
You study – Dan studies English twice a week.
but:
We play –Sharon plays football 3 times a week.