be afraid of doing sth
(1) 擔(dān)心會(huì)發(fā)生某事或某情況(但實(shí)際上未必會(huì)發(fā)生).如：
She was afraid of waking her husband.她怕吵醒她丈夫.
I was afraid of hurting her feelings.我怕傷害她的感情.
be afraid of doing sth 表示擔(dān)心會(huì)發(fā)生某事或某情況時(shí),其后也可用 be afraid that 替換.如：
He was afraid of losing face.＝He was afraid (that) he’d lose face.他怕失面zi.
(2) 害怕做某事或不敢做某事(指缺乏勇氣或害怕其后果而不敢).如：
I’m afraid of telling her.我不敢告訴她.
He was afraid of jumping.他不敢跳.
be afraid to do sth的意思是：害怕做某事或不敢做某事.如：
He was afraid to fly in a plane.他不敢坐飛機(jī).
He was afraid to go into the house and meet his father.他不敢進(jìn)屋去見他父親.
注：以上兩類句型的異同之處：表示擔(dān)心會(huì)發(fā)生某事或某情況,只能用 be afraid of doing sth,而表示害怕做某事或不敢做某事等,則兩者都可用.如：
Don’t be afraid to ask [of asking] question.不要害怕問問題.
He is afraid to go out [of going out] alone at night.他不敢晚上一個(gè)人出去
綜上,你那句子是表示害怕看見蛇,因此都可以用