Learn Spanish (Latin America): ¿Sientes eso?

Sientes comes from the verb sentir (to feel). It is a stem-changing verb, which is exactly what this lesson covers! When you conjugate it, the e in the stem changes to ie for most forms, including the informal "you" (tú) form. That is why it becomes tú sientes.

How do we know this means "Do you feel" when the word for "you" isn't there?

In Spanish, the ending of the verb tells you who is doing the action. The -es ending in sientes specifically belongs to the informal "you" (tú). Because the verb ending makes it perfectly clear who you are talking to, the pronoun tú is optional and usually left out.

Why does the sentence use eso for "that" instead of ese or esa?

We use the neuter pronoun eso when "that" refers to an unknown object, a general idea, or a situation. If you were talking about a specific masculine or feminine noun, you would use ese or esa (like ese libro for "that book"). Since the speaker is asking about a vague sensation, sound, or occurrence, eso is the correct choice.

Why is there no word for "Do" in the Spanish sentence?