While he was taking a shower, his dogs were eating his steaks.
(That is the correct sentence according to the website that I visited.)
We use the past progressive with the past progressive to show two actions in progress at the same time.
But, can I also say:
"While he was taking a shower, his dogs ate his steaks."?
(That sentence is wrong according to the website that I visited.)
In my opinion, the action (was taking) was still in progress when the second action (ate) happened.
The past progressive tense is used to describe an on-going action that occurred at some time in the past, ie the action occurred over a period of time. The actual length of that time may or may not be specified. The action may or may not have been completed.
The past tense is used to describe an event that occurred at some time in the past. The duration of that event is irrelevant; the event is effectively treated as if it occurred at a moment in time. The event is always regarded as having been completed.
If you are talking about two actions in the past that are in progress simultaneously, then you must use the past progressive tense to describe both actions. In this case your original sentence would need to be used.
If you are talking about an event in the past that occurred simultaneously with an action that was in progress, then you should use the past tense to describe the event while using the past progressive tense to describe the action in progress. For example:
While he was taking a shower, his dogs ate his steaks.
or
His dogs ate his steaks while he was taking a shower.
If you are talking about two events that occurred simultaneously in the past, then you should use the past tense to describe both events. For example:
When he took his shower, his dogs ate his steaks.
or
His dogs ate his takes when he took a shower.
You should note that I changed 'while' to 'when' in my last two examples. Simultaneous clauses are often linked with the use of 'when' or 'while'. Other links such as 'and' or 'as' are also frequently used. Because 'while' indicates that a period of time has elapsed, it is frequently used at the beginning of a clause that uses the past progressive tense, and is rarely used at the beginning of a clause that uses the simple past tense. On the other hand, 'when' is rarely used at the beginning of a clause that uses the past progressive tense, and is frequently used at the beginning of a clause that uses the simple past tense.
With simple past ate the sentence means that the dogs devoured his steaks at some time during his shower.
With were eating the sentence means that his showering and their devouring were ongoing at the same time. The sentence doesn't mean that it took him exactly the same amount of time to shower as it took them to devour his steaks. There was simply an overlap of the two ongoing activities.
P.S. Let's assume they were tiny dogs to make this part clearer. Those dogs didn't wolf the steaks down in one gulp; rather, they nibbled away at the steaks. Even though it may have taken them some time to devour the steaks, the simple present ate is not concerned about the action as something that took some time; rather it casts the action merely as something that happened, not as an ongoing activity.
Think about it this way: while I was talking on the phone, someone knocked on my door. The second clause has to be in the simple past because the person was not literally knocking on the door the whole time that the person was talking on the phone. Now if one was in the process of knocking on the door when something else happened we could use: I was knocking. For example, I heard a loud bang from inside her room when I was knocking on her door. OR While I was knocking on her door, I heard a loud bang from inside her room.
