As Glenn-san pointed out, the sentenses 床を走るを見ました。, 走るが好きです。 are not grammatically correct, at least in modern Japanese. You can say (何かが)床を走るのを見ました。, 走るのが好きです。 with using the nominalizer の. In a grammatical point of view, 床を走るもの is a noun phrase that the clause 床を走る is modifying the pronoun もの, whereas (何かが)床を走るの is a noun clause which is nominalized by の.
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EDIT:
こと in 走ること is considered as a nominalizer.
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In archaic grammar, a clause can be used as a noun without the nominalizer, 我昨夜何者か床を走るを見たり or something like that.;-)