can you see it
IN THIS SENTENCE FIND THE MISTAKE

There is no mistake (unless you don't like dogs). 'I found a dog' is perfectly correct if you are talking about something that you did in the past as in "I was passing a car and heard a noise, there, under the wheel arch, I found a dog.". An alternative 'I've found a dog' implies that you are actually in the process of finding a dog or that you have just found one a few minutes ago.
Of course the original poster is from the USA so he could mean anything.
And then again, the OP could have started the sentence with a small L in which case it is not a mistake, merely illiteracy.

There is no mistake (unless you don't like dogs). 'I found a dog' is perfectly correct if you are talking about something that you did in the past as in "I was passing a car and heard a noise, there, under the wheel arch, I found a dog.". An alternative 'I've found a dog' implies that you are actually in the process of finding a dog or that you have just found one a few minutes ago.
it is not a i it is a L
l found a dog.