Learn Icelandic: Heyrðir þú hvað hann spurði?

Icelandic doesn't use helper verbs like "do" or "did" to make questions. Instead, you simply swap the subject and the verb. So, "Did you hear?" becomes Heyrðir þú? (literally "Heard you?").

Why does heyrðir end in -ðir?

This is the simple past tense of the weak verb heyra (to hear). It takes the -ði past tense marker. Because the subject is þú (you), we add an -r at the very end, making it heyrðir.

The dictionary form of "to ask" is spyrja. Why does it become spurði here?

Spyrja is a weak verb, but it belongs to a special group that drops the -j- and changes its vowel in the past tense (here, from y to u). It uses the -ði ending, so hann spyr (he asks) becomes hann spurði (he asked).

Why doesn't spurði have an -r at the end like heyrðir does?